你的树每一层需要两倍的距离:

       a
      / \
     /   \
    /     \
   /       \
   b       c
  / \     / \
 /   \   /   \
 d   e   f   g
/ \ / \ / \ / \
h i j k l m n o

你可以将你的树保存在一个数组的数组中，每个数组对应一个深度:

[[a],[b,c],[d,e,f,g],[h,i,j,k,l,m,n,o]]

如果你的树没有满，你需要在数组中包含空值:

       a
      / \
     /   \
    /     \
   /       \
   b       c
  / \     / \
 /   \   /   \
 d   e   f   g
/ \   \ / \   \
h i   k l m   o
[[a],[b,c],[d,e,f,g],[h,i, ,k,l,m, ,o]]

然后你可以遍历数组来打印你的树，根据深度打印第一个元素之前和元素之间的空格，根据下一层数组中对应的元素是否被填充打印行。 如果您的值可以超过一个字符长，您需要在创建数组表示时找到最长的值，并相应地乘以所有宽度和行数。

我已经创建了简单的二叉树打印机。您可以随心所欲地使用和修改它，但无论如何它都没有优化。我认为这里有很多东西可以改进;)

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class BTreePrinterTest {

    private static Node<Integer> test1() {
        Node<Integer> root = new Node<Integer>(2);
        Node<Integer> n11 = new Node<Integer>(7);
        Node<Integer> n12 = new Node<Integer>(5);
        Node<Integer> n21 = new Node<Integer>(2);
        Node<Integer> n22 = new Node<Integer>(6);
        Node<Integer> n23 = new Node<Integer>(3);
        Node<Integer> n24 = new Node<Integer>(6);
        Node<Integer> n31 = new Node<Integer>(5);
        Node<Integer> n32 = new Node<Integer>(8);
        Node<Integer> n33 = new Node<Integer>(4);
        Node<Integer> n34 = new Node<Integer>(5);
        Node<Integer> n35 = new Node<Integer>(8);
        Node<Integer> n36 = new Node<Integer>(4);
        Node<Integer> n37 = new Node<Integer>(5);
        Node<Integer> n38 = new Node<Integer>(8);

        root.left = n11;
        root.right = n12;

        n11.left = n21;
        n11.right = n22;
        n12.left = n23;
        n12.right = n24;

        n21.left = n31;
        n21.right = n32;
        n22.left = n33;
        n22.right = n34;
        n23.left = n35;
        n23.right = n36;
        n24.left = n37;
        n24.right = n38;

        return root;
    }

    private static Node<Integer> test2() {
        Node<Integer> root = new Node<Integer>(2);
        Node<Integer> n11 = new Node<Integer>(7);
        Node<Integer> n12 = new Node<Integer>(5);
        Node<Integer> n21 = new Node<Integer>(2);
        Node<Integer> n22 = new Node<Integer>(6);
        Node<Integer> n23 = new Node<Integer>(9);
        Node<Integer> n31 = new Node<Integer>(5);
        Node<Integer> n32 = new Node<Integer>(8);
        Node<Integer> n33 = new Node<Integer>(4);

        root.left = n11;
        root.right = n12;

        n11.left = n21;
        n11.right = n22;

        n12.right = n23;
        n22.left = n31;
        n22.right = n32;

        n23.left = n33;

        return root;
    }

    public static void main(String[] args) {

        BTreePrinter.printNode(test1());
        BTreePrinter.printNode(test2());

    }
}

class Node<T extends Comparable<?>> {
    Node<T> left, right;
    T data;

    public Node(T data) {
        this.data = data;
    }
}

class BTreePrinter {

    public static <T extends Comparable<?>> void printNode(Node<T> root) {
        int maxLevel = BTreePrinter.maxLevel(root);

        printNodeInternal(Collections.singletonList(root), 1, maxLevel);
    }

    private static <T extends Comparable<?>> void printNodeInternal(List<Node<T>> nodes, int level, int maxLevel) {
        if (nodes.isEmpty() || BTreePrinter.isAllElementsNull(nodes))
            return;

        int floor = maxLevel - level;
        int endgeLines = (int) Math.pow(2, (Math.max(floor - 1, 0)));
        int firstSpaces = (int) Math.pow(2, (floor)) - 1;
        int betweenSpaces = (int) Math.pow(2, (floor + 1)) - 1;

        BTreePrinter.printWhitespaces(firstSpaces);

        List<Node<T>> newNodes = new ArrayList<Node<T>>();
        for (Node<T> node : nodes) {
            if (node != null) {
                System.out.print(node.data);
                newNodes.add(node.left);
                newNodes.add(node.right);
            } else {
                newNodes.add(null);
                newNodes.add(null);
                System.out.print(" ");
            }

            BTreePrinter.printWhitespaces(betweenSpaces);
        }
        System.out.println("");

        for (int i = 1; i <= endgeLines; i++) {
            for (int j = 0; j < nodes.size(); j++) {
                BTreePrinter.printWhitespaces(firstSpaces - i);
                if (nodes.get(j) == null) {
                    BTreePrinter.printWhitespaces(endgeLines + endgeLines + i + 1);
                    continue;
                }

                if (nodes.get(j).left != null)
                    System.out.print("/");
                else
                    BTreePrinter.printWhitespaces(1);

                BTreePrinter.printWhitespaces(i + i - 1);

                if (nodes.get(j).right != null)
                    System.out.print("\\");
                else
                    BTreePrinter.printWhitespaces(1);

                BTreePrinter.printWhitespaces(endgeLines + endgeLines - i);
            }

            System.out.println("");
        }

        printNodeInternal(newNodes, level + 1, maxLevel);
    }

    private static void printWhitespaces(int count) {
        for (int i = 0; i < count; i++)
            System.out.print(" ");
    }

    private static <T extends Comparable<?>> int maxLevel(Node<T> node) {
        if (node == null)
            return 0;

        return Math.max(BTreePrinter.maxLevel(node.left), BTreePrinter.maxLevel(node.right)) + 1;
    }

    private static <T> boolean isAllElementsNull(List<T> list) {
        for (Object object : list) {
            if (object != null)
                return false;
        }

        return true;
    }

}

输出1:

         2               
        / \       
       /   \      
      /     \     
     /       \    
     7       5       
    / \     / \   
   /   \   /   \  
   2   6   3   6   
  / \ / \ / \ / \ 
  5 8 4 5 8 4 5 8 

输出2:

       2               
      / \       
     /   \      
    /     \     
   /       \    
   7       5       
  / \       \   
 /   \       \  
 2   6       9   
    / \     /   
    5 8     4   

按行打印[大]树。

输出的例子:

z
├── c
│   ├── a
│   └── b
├── d
├── e
│   └── asdf
└── f

代码:

public class TreeNode {

    final String name;
    final List<TreeNode> children;

    public TreeNode(String name, List<TreeNode> children) {
        this.name = name;
        this.children = children;
    }

    public String toString() {
        StringBuilder buffer = new StringBuilder(50);
        print(buffer, "", "");
        return buffer.toString();
    }

    private void print(StringBuilder buffer, String prefix, String childrenPrefix) {
        buffer.append(prefix);
        buffer.append(name);
        buffer.append('\n');
        for (Iterator<TreeNode> it = children.iterator(); it.hasNext();) {
            TreeNode next = it.next();
            if (it.hasNext()) {
                next.print(buffer, childrenPrefix + "├── ", childrenPrefix + "│   ");
            } else {
                next.print(buffer, childrenPrefix + "└── ", childrenPrefix + "    ");
            }
        }
    }
}

附注:这个答案并不完全关注“二叉”树——相反，它打印了各种类型的树。解决方案的灵感来自linux中的“树”命令。

迈克尔。克鲁兹曼，我不得不说，这人不错。这很有用。

然而，上面的方法只适用于个位数:如果您要使用多个数字，结构将会错位，因为您使用的是空格而不是制表符。

至于我后来的代码，我需要更多的数字，所以我自己编写了一个程序。

它现在有一些bug，现在我感觉很懒去纠正它们，但它打印得非常漂亮，节点可以接受更大数量的数字。

这棵树不会像问题提到的那样，但它旋转了270度:)

public static void printBinaryTree(TreeNode root, int level){
    if(root==null)
         return;
    printBinaryTree(root.right, level+1);
    if(level!=0){
        for(int i=0;i<level-1;i++)
            System.out.print("|\t");
        System.out.println("|-------"+root.val);
    }
    else
        System.out.println(root.val);
    printBinaryTree(root.left, level+1);
}    

将此函数与您自己指定的TreeNode一起放置，并保持初始级别为0，并享受!

以下是一些输出示例:

|       |       |-------11
|       |-------10
|       |       |-------9
|-------8
|       |       |-------7
|       |-------6
|       |       |-------5
4
|       |-------3
|-------2
|       |-------1


|       |       |       |-------10
|       |       |-------9
|       |-------8
|       |       |-------7
|-------6
|       |-------5
4
|       |-------3
|-------2
|       |-------1

唯一的问题是延伸的分支;我会尽快解决这个问题，但在此之前你也可以使用它。

我需要在我的一个项目中打印一个二叉树，为此我准备了一个java类TreePrinter，其中一个示例输出是:

                [+]
               /   \
              /     \
             /       \
            /         \
           /           \
        [*]             \
       /   \             [-]
[speed]     [2]         /   \
                    [45]     [12]

下面是TreePrinter类和TextNode类的代码。为了打印任何树，你可以用TextNode类创建一个等效的树。

import java.util.ArrayList;

public class TreePrinter {

    public TreePrinter(){
    }

    public static String TreeString(TextNode root){
        ArrayList layers = new ArrayList();
        ArrayList bottom = new ArrayList();

        FillBottom(bottom, root);  DrawEdges(root);

        int height = GetHeight(root);
        for(int i = 0; i  s.length()) min = s.length();

            if(!n.isEdge) s += "[";
            s += n.text;
            if(!n.isEdge) s += "]";

            layers.set(n.depth, s);
        }

        StringBuilder sb = new StringBuilder();

        for(int i = 0; i  temp = new ArrayList();

            for(int i = 0; i  0) temp.get(i-1).left = x;
                temp.add(x);
            }

            temp.get(count-1).left = n.left;
            n.left.depth = temp.get(count-1).depth+1;
            n.left = temp.get(0);

            DrawEdges(temp.get(count-1).left);
        }
        if(n.right != null){
            int count = n.right.x - (n.x + n.text.length() + 2);
            ArrayList temp = new ArrayList();

            for(int i = 0; i  0) temp.get(i-1).right = x;
                temp.add(x);
            }

            temp.get(count-1).right = n.right;
            n.right.depth = temp.get(count-1).depth+1;
            n.right = temp.get(0);  

            DrawEdges(temp.get(count-1).right);
        }
    }

    private static void FillBottom(ArrayList bottom, TextNode n){
        if(n == null) return;

        FillBottom(bottom, n.left);

        if(!bottom.isEmpty()){            
            int i = bottom.size()-1;
            while(bottom.get(i).isEdge) i--;
            TextNode last = bottom.get(i);

            if(!n.isEdge) n.x = last.x + last.text.length() + 3;
        }
        bottom.add(n);
        FillBottom(bottom, n.right);
    }

    private static boolean isLeaf(TextNode n){
        return (n.left == null && n.right == null);
    }

    private static int GetHeight(TextNode n){
        if(n == null) return 0;

        int l = GetHeight(n.left);
        int r = GetHeight(n.right);

        return Math.max(l, r) + 1;
    }
}


class TextNode {
    public String text;
    public TextNode parent, left, right;
    public boolean isEdge;
    public int x, depth;

    public TextNode(String text){
        this.text = text;
        parent = null; left = null; right = null;
        isEdge = false;
        x = 0; depth = 0;
    }
}

最后，这里是一个打印给定样本的测试类:

public class Test {

    public static void main(String[] args){
        TextNode root = new TextNode("+");
        root.left = new TextNode("*");            root.left.parent = root;
        root.right = new TextNode("-");           root.right.parent = root;
        root.left.left = new TextNode("speed");   root.left.left.parent = root.left;
        root.left.right = new TextNode("2");      root.left.right.parent = root.left;
        root.right.left = new TextNode("45");     root.right.left.parent = root.right;
        root.right.right = new TextNode("12");    root.right.right.parent = root.right;

        System.out.println(TreePrinter.TreeString(root));
    }
}

public static class Node<T extends Comparable<T>> {
    T value;
    Node<T> left, right;

    public void insertToTree(T v) {
        if (value == null) {
            value = v;
            return;
        }
        if (v.compareTo(value) < 0) {
            if (left == null) {
                left = new Node<T>();
            }
            left.insertToTree(v);
        } else {
            if (right == null) {
                right = new Node<T>();
            }
            right.insertToTree(v);
        }
    }

    public void printTree(OutputStreamWriter out) throws IOException {
        if (right != null) {
            right.printTree(out, true, "");
        }
        printNodeValue(out);
        if (left != null) {
            left.printTree(out, false, "");
        }
    }
    private void printNodeValue(OutputStreamWriter out) throws IOException {
        if (value == null) {
            out.write("<null>");
        } else {
            out.write(value.toString());
        }
        out.write('\n');
    }
    // use string and not stringbuffer on purpose as we need to change the indent at each recursion
    private void printTree(OutputStreamWriter out, boolean isRight, String indent) throws IOException {
        if (right != null) {
            right.printTree(out, true, indent + (isRight ? "        " : " |      "));
        }
        out.write(indent);
        if (isRight) {
            out.write(" /");
        } else {
            out.write(" \\");
        }
        out.write("----- ");
        printNodeValue(out);
        if (left != null) {
            left.printTree(out, false, indent + (isRight ? " |      " : "        "));
        }
    }

}

将打印:

                 /----- 20
                 |       \----- 15
         /----- 14
         |       \----- 13
 /----- 12
 |       |       /----- 11
 |       \----- 10
 |               \----- 9
8
 |               /----- 7
 |       /----- 6
 |       |       \----- 5
 \----- 4
         |       /----- 3
         \----- 2
                 \----- 1

对于输入

8 4 12 2 6 10 14 1 3 5 7 9 11 13 20 15

这是@anurag回答的一个变体——看到额外的|让我很烦

这是打印树的一个非常简单的解决方案。它不是那么漂亮，但它真的很简单:

enum { kWidth = 6 };
void PrintSpace(int n)
{
  for (int i = 0; i < n; ++i)
    printf(" ");
}

void PrintTree(struct Node * root, int level)
{
  if (!root) return;
  PrintTree(root->right, level + 1);
  PrintSpace(level * kWidth);
  printf("%d", root->data);
  PrintTree(root->left, level + 1);
}

样例输出:

      106
            105
104
            103
                  102
                        101
      100

public void printPreety() {
    List<TreeNode> list = new ArrayList<TreeNode>();
    list.add(head);
    printTree(list, getHeight(head));
}

public int getHeight(TreeNode head) {

    if (head == null) {
        return 0;
    } else {
        return 1 + Math.max(getHeight(head.left), getHeight(head.right));
    }
}

/**
 * pass head node in list and height of the tree 
 * 
 * @param levelNodes
 * @param level
 */
private void printTree(List<TreeNode> levelNodes, int level) {

    List<TreeNode> nodes = new ArrayList<TreeNode>();

    //indentation for first node in given level
    printIndentForLevel(level);

    for (TreeNode treeNode : levelNodes) {

        //print node data
        System.out.print(treeNode == null?" ":treeNode.data);

        //spacing between nodes
        printSpacingBetweenNodes(level);

        //if its not a leaf node
        if(level>1){
            nodes.add(treeNode == null? null:treeNode.left);
            nodes.add(treeNode == null? null:treeNode.right);
        }
    }
    System.out.println();

    if(level>1){        
        printTree(nodes, level-1);
    }
}

private void printIndentForLevel(int level){
    for (int i = (int) (Math.pow(2,level-1)); i >0; i--) {
        System.out.print(" ");
    }
}

private void printSpacingBetweenNodes(int level){
    //spacing between nodes
    for (int i = (int) ((Math.pow(2,level-1))*2)-1; i >0; i--) {
        System.out.print(" ");
    }
}


Prints Tree in following format:
                4                               
        3               7               
    1               5       8       
      2                       10   
                             9   

改编自Vasya Novikov的答案，使其更二进制，并使用StringBuilder提高效率(在Java中将String对象连接在一起通常效率很低)。

public StringBuilder toString(StringBuilder prefix, boolean isTail, StringBuilder sb) {
    if(right!=null) {
        right.toString(new StringBuilder().append(prefix).append(isTail ? "│   " : "    "), false, sb);
    }
    sb.append(prefix).append(isTail ? "└── " : "┌── ").append(value.toString()).append("\n");
    if(left!=null) {
        left.toString(new StringBuilder().append(prefix).append(isTail ? "    " : "│   "), true, sb);
    }
    return sb;
}

@Override
public String toString() {
    return this.toString(new StringBuilder(), true, new StringBuilder()).toString();
}

输出:

│       ┌── 7
│   ┌── 6
│   │   └── 5
└── 4
    │   ┌── 3
    └── 2
        └── 1
            └── 0

我为此做了一个改进的算法，可以很好地处理不同大小的节点。它使用行自上而下地打印。

package alg;

import java.util.ArrayList;
import java.util.List;


/**
 * Binary tree printer
 * 
 * @author MightyPork
 */
public class TreePrinter
{
    /** Node that can be printed */
    public interface PrintableNode
    {
        /** Get left child */
        PrintableNode getLeft();


        /** Get right child */
        PrintableNode getRight();


        /** Get text to be printed */
        String getText();
    }


    /**
     * Print a tree
     * 
     * @param root
     *            tree root node
     */
    public static void print(PrintableNode root)
    {
        List<List<String>> lines = new ArrayList<List<String>>();

        List<PrintableNode> level = new ArrayList<PrintableNode>();
        List<PrintableNode> next = new ArrayList<PrintableNode>();

        level.add(root);
        int nn = 1;

        int widest = 0;

        while (nn != 0) {
            List<String> line = new ArrayList<String>();

            nn = 0;

            for (PrintableNode n : level) {
                if (n == null) {
                    line.add(null);

                    next.add(null);
                    next.add(null);
                } else {
                    String aa = n.getText();
                    line.add(aa);
                    if (aa.length() > widest) widest = aa.length();

                    next.add(n.getLeft());
                    next.add(n.getRight());

                    if (n.getLeft() != null) nn++;
                    if (n.getRight() != null) nn++;
                }
            }

            if (widest % 2 == 1) widest++;

            lines.add(line);

            List<PrintableNode> tmp = level;
            level = next;
            next = tmp;
            next.clear();
        }

        int perpiece = lines.get(lines.size() - 1).size() * (widest + 4);
        for (int i = 0; i < lines.size(); i++) {
            List<String> line = lines.get(i);
            int hpw = (int) Math.floor(perpiece / 2f) - 1;

            if (i > 0) {
                for (int j = 0; j < line.size(); j++) {

                    // split node
                    char c = ' ';
                    if (j % 2 == 1) {
                        if (line.get(j - 1) != null) {
                            c = (line.get(j) != null) ? '┴' : '┘';
                        } else {
                            if (j < line.size() && line.get(j) != null) c = '└';
                        }
                    }
                    System.out.print(c);

                    // lines and spaces
                    if (line.get(j) == null) {
                        for (int k = 0; k < perpiece - 1; k++) {
                            System.out.print(" ");
                        }
                    } else {

                        for (int k = 0; k < hpw; k++) {
                            System.out.print(j % 2 == 0 ? " " : "─");
                        }
                        System.out.print(j % 2 == 0 ? "┌" : "┐");
                        for (int k = 0; k < hpw; k++) {
                            System.out.print(j % 2 == 0 ? "─" : " ");
                        }
                    }
                }
                System.out.println();
            }

            // print line of numbers
            for (int j = 0; j < line.size(); j++) {

                String f = line.get(j);
                if (f == null) f = "";
                int gap1 = (int) Math.ceil(perpiece / 2f - f.length() / 2f);
                int gap2 = (int) Math.floor(perpiece / 2f - f.length() / 2f);

                // a number
                for (int k = 0; k < gap1; k++) {
                    System.out.print(" ");
                }
                System.out.print(f);
                for (int k = 0; k < gap2; k++) {
                    System.out.print(" ");
                }
            }
            System.out.println();

            perpiece /= 2;
        }
    }
}

要在树中使用它，让Node类实现PrintableNode。

示例输出:

                                         2952:0                                             
                    ┌───────────────────────┴───────────────────────┐                       
                 1249:-1                                         5866:0                     
        ┌───────────┴───────────┐                       ┌───────────┴───────────┐           
     491:-1                  1572:0                  4786:1                  6190:0         
  ┌─────┘                                               └─────┐           ┌─────┴─────┐     
339:0                                                      5717:0      6061:0      6271:0   

private StringBuilder prettyPrint(Node root, int currentHeight, int totalHeight) {
        StringBuilder sb = new StringBuilder();
        int spaces = getSpaceCount(totalHeight-currentHeight + 1);
        if(root == null) {
            //create a 'spatial' block and return it
            String row = String.format("%"+(2*spaces+1)+"s%n", "");
            //now repeat this row space+1 times
            String block = new String(new char[spaces+1]).replace("\0", row);
            return new StringBuilder(block);
        }
        if(currentHeight==totalHeight) return new StringBuilder(root.data+"");
        int slashes = getSlashCount(totalHeight-currentHeight +1);
        sb.append(String.format("%"+(spaces+1)+"s%"+spaces+"s", root.data+"", ""));
        sb.append("\n");
        //now print / and \
        // but make sure that left and right exists
        char leftSlash = root.left == null? ' ':'/';
        char rightSlash = root.right==null? ' ':'\\';
        int spaceInBetween = 1;
        for(int i=0, space = spaces-1; i<slashes; i++, space --, spaceInBetween+=2) {
            for(int j=0; j<space; j++) sb.append(" ");
            sb.append(leftSlash);
            for(int j=0; j<spaceInBetween; j++) sb.append(" ");
            sb.append(rightSlash+"");
            for(int j=0; j<space; j++) sb.append(" ");
            sb.append("\n");
        }
        //sb.append("\n");

        //now get string representations of left and right subtrees
        StringBuilder leftTree = prettyPrint(root.left, currentHeight+1, totalHeight);
        StringBuilder rightTree = prettyPrint(root.right, currentHeight+1, totalHeight);
        // now line by line print the trees side by side
        Scanner leftScanner = new Scanner(leftTree.toString());
        Scanner rightScanner = new Scanner(rightTree.toString());
//      spaceInBetween+=1;
        while(leftScanner.hasNextLine()) {
            if(currentHeight==totalHeight-1) {
                sb.append(String.format("%-2s %2s", leftScanner.nextLine(), rightScanner.nextLine()));
                sb.append("\n");
                spaceInBetween-=2;              
            }
            else {
                sb.append(leftScanner.nextLine());
                sb.append(" ");
                sb.append(rightScanner.nextLine()+"\n");
            }
        }

        return sb;

    }
private int getSpaceCount(int height) {
        return (int) (3*Math.pow(2, height-2)-1);
    }
private int getSlashCount(int height) {
        if(height <= 3) return height -1;
        return (int) (3*Math.pow(2, height-3)-1);
    }

https://github.com/murtraja/java-binary-tree-printer

只适用于1到2位整数(我懒得让它通用)

在控制台打印:

                                                500
                       700                                             300   
    200                                   400                                                                                          

简单代码:

public int getHeight()
    {
        if(rootNode == null) return -1;
        return getHeight(rootNode);
    }

    private int getHeight(Node node)
    {
        if(node == null) return -1;

        return Math.max(getHeight(node.left), getHeight(node.right)) + 1;
    }

    public void printBinaryTree(Node rootNode)
    {
        Queue<Node> rootsQueue = new LinkedList<Node>();
        Queue<Node> levelQueue = new LinkedList<Node>();
        levelQueue.add(rootNode);
        int treeHeight = getHeight();
        int firstNodeGap;
        int internalNodeGap;
        int copyinternalNodeGap;
        while(true)
        {
            System.out.println("");
            internalNodeGap = (int)(Math.pow(2, treeHeight + 1) -1);  
            copyinternalNodeGap = internalNodeGap;
            firstNodeGap = internalNodeGap/2;

            boolean levelFirstNode = true;

            while(!levelQueue.isEmpty())
            {
                internalNodeGap = copyinternalNodeGap;
                Node currNode = levelQueue.poll();
                if(currNode != null)
                {
                    if(levelFirstNode)
                    {
                        while(firstNodeGap > 0)
                        {
                            System.out.format("%s", "   ");
                            firstNodeGap--; 
                        }
                        levelFirstNode =false;
                    }
                    else
                    {
                        while(internalNodeGap>0)
                        {
                            internalNodeGap--;
                            System.out.format("%s", "   ");
                        }
                    }
                    System.out.format("%3d",currNode.data);
                    rootsQueue.add(currNode);
                }
            }

            --treeHeight;

            while(!rootsQueue.isEmpty())
            {
                Node currNode = rootsQueue.poll();
                if(currNode != null)
                {
                    levelQueue.add(currNode.left);
                    levelQueue.add(currNode.right);
                }
            }

            if(levelQueue.isEmpty()) break;
        }

    }

这是一个非常多功能的树打印机。不是最好看的，但能处理很多案子。如果你能弄清楚，可以随意添加斜杠。

package com.tomac120.NodePrinter;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

/**
 * Created by elijah on 6/28/16.
 */
public class NodePrinter{
    final private List<List<PrintableNodePosition>> nodesByRow;
    int maxColumnsLeft = 0;
    int maxColumnsRight = 0;
    int maxTitleLength = 0;
    String sep = " ";
    int depth = 0;

    public NodePrinter(PrintableNode rootNode, int chars_per_node){
        this.setDepth(rootNode,1);
        nodesByRow = new ArrayList<>(depth);
        this.addNode(rootNode._getPrintableNodeInfo(),0,0);
        for (int i = 0;i<chars_per_node;i++){
            //sep += " ";
        }
    }

    private void setDepth(PrintableNode info, int depth){
        if (depth > this.depth){
            this.depth = depth;
        }
        if (info._getLeftChild() != null){
            this.setDepth(info._getLeftChild(),depth+1);
        }
        if (info._getRightChild() != null){
            this.setDepth(info._getRightChild(),depth+1);
        }
    }

    private void addNode(PrintableNodeInfo node, int level, int position){
        if (position < 0 && -position > maxColumnsLeft){
            maxColumnsLeft = -position;
        }
        if (position > 0 && position > maxColumnsRight){
            maxColumnsRight = position;
        }
        if (node.getTitleLength() > maxTitleLength){
           maxTitleLength = node.getTitleLength();
        }
        List<PrintableNodePosition> row = this.getRow(level);
        row.add(new PrintableNodePosition(node, level, position));
        level++;

        int depthToUse = Math.min(depth,6);
        int levelToUse = Math.min(level,6);
        int offset = depthToUse - levelToUse-1;
        offset = (int)(Math.pow(offset,Math.log(depthToUse)*1.4));
        offset = Math.max(offset,3);


        PrintableNodeInfo leftChild = node.getLeftChildInfo();
        PrintableNodeInfo rightChild = node.getRightChildInfo();
        if (leftChild != null){
            this.addNode(leftChild,level,position-offset);
        }
        if (rightChild != null){
            this.addNode(rightChild,level,position+offset);
        }
    }

    private List<PrintableNodePosition> getRow(int row){
        if (row > nodesByRow.size() - 1){
            nodesByRow.add(new LinkedList<>());
        }
        return nodesByRow.get(row);
    }

    public void print(){
        int max_chars = this.maxColumnsLeft+maxColumnsRight+1;
        int level = 0;
        String node_format = "%-"+this.maxTitleLength+"s";
        for (List<PrintableNodePosition> pos_arr : this.nodesByRow){
            String[] chars = this.getCharactersArray(pos_arr,max_chars);
            String line = "";
            int empty_chars = 0;
            for (int i=0;i<chars.length+1;i++){
                String value_i = i < chars.length ? chars[i]:null;
                if (chars.length + 1 == i || value_i != null){
                    if (empty_chars > 0) {
                        System.out.print(String.format("%-" + empty_chars + "s", " "));
                    }
                    if (value_i != null){
                        System.out.print(String.format(node_format,value_i));
                        empty_chars = -1;
                    } else{
                        empty_chars = 0;
                    }
                } else {
                    empty_chars++;
                }
            }
            System.out.print("\n");

            int depthToUse = Math.min(6,depth);
            int line_offset = depthToUse - level;
            line_offset *= 0.5;
            line_offset = Math.max(0,line_offset);

            for (int i=0;i<line_offset;i++){
                System.out.println("");
            }


            level++;
        }
    }

    private String[] getCharactersArray(List<PrintableNodePosition> nodes, int max_chars){
        String[] positions = new String[max_chars+1];
        for (PrintableNodePosition a : nodes){
            int pos_i = maxColumnsLeft + a.column;
            String title_i = a.nodeInfo.getTitleFormatted(this.maxTitleLength);
            positions[pos_i] = title_i;
        }
        return positions;
    }
}

NodeInfo类

package com.tomac120.NodePrinter;

/**
 * Created by elijah on 6/28/16.
 */
public class PrintableNodeInfo {
    public enum CLI_PRINT_COLOR {
        RESET("\u001B[0m"),
        BLACK("\u001B[30m"),
        RED("\u001B[31m"),
        GREEN("\u001B[32m"),
        YELLOW("\u001B[33m"),
        BLUE("\u001B[34m"),
        PURPLE("\u001B[35m"),
        CYAN("\u001B[36m"),
        WHITE("\u001B[37m");

        final String value;
        CLI_PRINT_COLOR(String value){
            this.value = value;
        }

        @Override
        public String toString() {
            return value;
        }
    }
    private final String title;
    private final PrintableNode leftChild;
    private final PrintableNode rightChild;
    private final CLI_PRINT_COLOR textColor;

    public PrintableNodeInfo(String title, PrintableNode leftChild, PrintableNode rightChild){
        this(title,leftChild,rightChild,CLI_PRINT_COLOR.BLACK);
    }

    public PrintableNodeInfo(String title, PrintableNode leftChild, PrintableNode righthild, CLI_PRINT_COLOR textColor){
        this.title = title;
        this.leftChild = leftChild;
        this.rightChild = righthild;
        this.textColor = textColor;
    }

    public String getTitle(){
        return title;
    }

    public CLI_PRINT_COLOR getTextColor(){
        return textColor;
    }

    public String getTitleFormatted(int max_chars){
        return this.textColor+title+CLI_PRINT_COLOR.RESET;
        /*
        String title = this.title.length() > max_chars ? this.title.substring(0,max_chars+1):this.title;
        boolean left = true;
        while(title.length() < max_chars){
            if (left){
                title = " "+title;
            } else {
                title = title + " ";
            }
        }
        return this.textColor+title+CLI_PRINT_COLOR.RESET;*/
    }

    public int getTitleLength(){
        return title.length();
    }

    public PrintableNodeInfo getLeftChildInfo(){
        if (leftChild == null){
            return null;
        }
        return leftChild._getPrintableNodeInfo();
    }

    public PrintableNodeInfo getRightChildInfo(){
        if (rightChild == null){
            return null;
        }
        return rightChild._getPrintableNodeInfo();
    }
}

NodePosition类

package com.tomac120.NodePrinter;

/**
 * Created by elijah on 6/28/16.
 */
public class PrintableNodePosition implements Comparable<PrintableNodePosition> {
    public final int row;
    public final int column;
    public final PrintableNodeInfo nodeInfo;
    public PrintableNodePosition(PrintableNodeInfo nodeInfo, int row, int column){
        this.row = row;
        this.column = column;
        this.nodeInfo = nodeInfo;
    }

    @Override
    public int compareTo(PrintableNodePosition o) {
        return Integer.compare(this.column,o.column);
    }
}

最后是节点接口

package com.tomac120.NodePrinter;

/**
 * Created by elijah on 6/28/16.
 */
public interface PrintableNode {
    PrintableNodeInfo _getPrintableNodeInfo();
    PrintableNode _getLeftChild();
    PrintableNode _getRightChild();
}

一个Scala解决方案，改编自Vasya Novikov的答案，专门用于二叉树:

/** An immutable Binary Tree. */
case class BTree[T](value: T, left: Option[BTree[T]], right: Option[BTree[T]]) {

  /* Adapted from: http://stackoverflow.com/a/8948691/643684 */
  def pretty: String = {
    def work(tree: BTree[T], prefix: String, isTail: Boolean): String = {
      val (line, bar) = if (isTail) ("└── ", " ") else ("├── ", "│")

      val curr = s"${prefix}${line}${tree.value}"

      val rights = tree.right match {
        case None    => s"${prefix}${bar}   ├── ∅"
        case Some(r) => work(r, s"${prefix}${bar}   ", false)
      }

      val lefts = tree.left match {
        case None    => s"${prefix}${bar}   └── ∅"
        case Some(l) => work(l, s"${prefix}${bar}   ", true)
      }

      s"${curr}\n${rights}\n${lefts}"

    }

    work(this, "", true)
  }
}

我发现VasyaNovikov的答案对于打印大型通用树非常有用，并将其修改为二叉树

代码:

class TreeNode {
    Integer data = null;
    TreeNode left = null;
    TreeNode right = null;

    TreeNode(Integer data) {this.data = data;}

    public void print() {
        print("", this, false);
    }

    public void print(String prefix, TreeNode n, boolean isLeft) {
        if (n != null) {
            System.out.println (prefix + (isLeft ? "|-- " : "\\-- ") + n.data);
            print(prefix + (isLeft ? "|   " : "    "), n.left, true);
            print(prefix + (isLeft ? "|   " : "    "), n.right, false);
        }
    }
}

样例输出:

\-- 7
    |-- 3
    |   |-- 1
    |   |   \-- 2
    |   \-- 5
    |       |-- 4
    |       \-- 6
    \-- 11
        |-- 9
        |   |-- 8
        |   \-- 10
        \-- 13
            |-- 12
            \-- 14

下面是可视化树的另一种方法:将节点保存为xml文件，然后让浏览器显示层次结构:

class treeNode{
    int key;
    treeNode left;
    treeNode right;

    public treeNode(int key){
        this.key = key;
        left = right = null;
    }

    public void printNode(StringBuilder output, String dir){
        output.append("<node key='" + key + "' dir='" + dir + "'>");
        if(left != null)
            left.printNode(output, "l");
        if(right != null)
            right.printNode(output, "r");
        output.append("</node>");
    }
}

class tree{
    private treeNode treeRoot;

    public tree(int key){
        treeRoot = new treeNode(key);
    }

    public void insert(int key){
        insert(treeRoot, key);
    }

    private treeNode insert(treeNode root, int key){
        if(root == null){
            treeNode child = new treeNode(key);
            return child;
        }

        if(key < root.key)
            root.left = insert(root.left, key);
        else if(key > root.key)
            root.right = insert(root.right, key);

        return root;
    }

    public void saveTreeAsXml(){
        StringBuilder strOutput = new StringBuilder();
        strOutput.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
        treeRoot.printNode(strOutput, "root");
        try {
            PrintWriter writer = new PrintWriter("C:/tree.xml", "UTF-8");
            writer.write(strOutput.toString());
            writer.close();
        }
        catch (FileNotFoundException e){

        }
        catch(UnsupportedEncodingException e){

        }
    }
}

下面是测试它的代码:

    tree t = new tree(1);
    t.insert(10);
    t.insert(5);
    t.insert(4);
    t.insert(20);
    t.insert(40);
    t.insert(30);
    t.insert(80);
    t.insert(60);
    t.insert(50);

    t.saveTreeAsXml();

输出如下所示:

根据VasyaNovikov的回答。改进了一些Java魔术:泛型和函数接口。

/**
 * Print a tree structure in a pretty ASCII fromat.
 * @param prefix Currnet previx. Use "" in initial call!
 * @param node The current node. Pass the root node of your tree in initial call.
 * @param getChildrenFunc A {@link Function} that returns the children of a given node.
 * @param isTail Is node the last of its sibblings. Use true in initial call. (This is needed for pretty printing.)
 * @param <T> The type of your nodes. Anything that has a toString can be used.
 */
private <T> void printTreeRec(String prefix, T node, Function<T, List<T>> getChildrenFunc, boolean isTail) {
    String nodeName = node.toString();
    String nodeConnection = isTail ? "└── " : "├── ";
    log.debug(prefix + nodeConnection + nodeName);
    List<T> children = getChildrenFunc.apply(node);
    for (int i = 0; i < children.size(); i++) {
        String newPrefix = prefix + (isTail ? "    " : "│   ");
        printTreeRec(newPrefix, children.get(i), getChildrenFunc, i == children.size()-1);
    }
}

初始调用示例:

Function<ChecksumModel, List<ChecksumModel>> getChildrenFunc = node -> getChildrenOf(node)
printTreeRec("", rootNode, getChildrenFunc, true);

将输出如下内容

└── rootNode
    ├── childNode1
    ├── childNode2
    │   ├── childNode2.1
    │   ├── childNode2.2
    │   └── childNode2.3
    ├── childNode3
    └── childNode4

这是水平视图最简单的解决方案。我举了很多例子。很适合我的目的。更新自@ ntin -k的回答。

public void print(String prefix, BTNode n, boolean isLeft) {
    if (n != null) {
        print(prefix + "     ", n.right, false);
        System.out.println (prefix + ("|-- ") + n.data);
        print(prefix + "     ", n.left, true);
    }
}

电话:

bst.print("", bst.root, false);

解决方案:

                         |-- 80
                    |-- 70
               |-- 60
          |-- 50
     |-- 40
|-- 30
     |-- 20
          |-- 10

using map...
{
Map<Integer,String> m = new LinkedHashMap<>();

         tn.printNodeWithLvl(node,l,m);

        for(Entry<Integer, String> map :m.entrySet()) {
            System.out.println(map.getValue());
        }
then....method


   private  void printNodeWithLvl(Node node,int l,Map<Integer,String> m) {
       if(node==null) {
           return;
       }
      if(m.containsKey(l)) {
          m.put(l, new StringBuilder(m.get(l)).append(node.value).toString());
      }else {
          m.put(l, node.value+"");
      }
      l++;
      printNodeWithLvl( node.left,l,m);
      printNodeWithLvl(node.right,l,m);

    }
}

与垂直表示相比，水平表示有点复杂。垂直打印只是简单的RNL(右->节点->左或镜像的顺序)遍历，以便先打印右子树，然后打印左子树。

def printFullTree(root, delim=' ', idnt=[], left=None):
    if root:
        idnt.append(delim)
        x, y = setDelims(left)
        printFullTree(root.right, x, idnt, False)
        indent2(root.val, idnt)
        printFullTree(root.left, y, idnt, True)
        idnt.pop()

def setDelims(left):
    x = ' '; y='|'
    return (y,x) if (left == True) else (x,y) if (left == False) else (x,x)

def indent2(x, idnt, width=6):
    for delim in idnt:
        print(delim + ' '*(width-1), end='')
    print('|->', x)

output:
                        |-> 15
                  |-> 14
                  |     |-> 13
            |-> 12
            |     |     |-> 11
            |     |-> 10
            |           |-> 9
      |-> 8
            |           |-> 7
            |     |-> 6
            |     |     |-> 4
            |-> 3
                  |     |-> 2
                  |-> 1
                        |-> 0

在水平表示中，显示由TreeMap的HashMap或HashMap<Integer, TreeMap<Integer, Object>> xy构建;其中HashMap包含节点的y轴/level_no作为Key, TreeMap作为value。Treemap内部保存同一级别的所有节点，按它们的x轴值排序，作为键，从最左端开始-ve，根=0，最右端=+ve。

如果使用自平衡树/Treap，则使用HashMap使算法在每个级别的O(1)查找中工作，并在O(logn)中使用TreeMap排序。

不过，在这样做的时候，不要忘记为空子存储占位符，例如' '/空格，这样树看起来就像预期的那样。

现在唯一剩下的就是计算水平节点的距离，这可以用一些数学计算来完成，

计算树的宽度和高度。 一旦完成，在显示节点时，根据计算的宽度，高度和倾斜信息(如果有的话)，以最佳距离呈现它们。

https://github.com/AharonSambol/PrettyPrintTreeJava

我知道我迟到了。但是我做了这个解决方案，不仅适用于简单的树，也适用于更复杂的树(如多行字符串)

示例输出:

试试这个:

public static void print(int[] minHeap, int minWidth) {

    int size = minHeap.length;

    int level = log2(size);
    int maxLength = (int) Math.pow(2, level) * minWidth;
    int currentLevel = -1 ;
    int width = maxLength;

    for (int i = 0; i < size; i++) {
        if (log2(i + 1) > currentLevel) {
            currentLevel++;
            System.out.println();
            width = maxLength / (int) Math.pow(2, currentLevel);
        }
        System.out.print(StringUtils.center(String.valueOf(minHeap[i]), width));
    }
    System.out.println();
}

private static int log2(int n) {
    return (int) (Math.log(n) / Math.log(2));
}

这段代码片段的思想是用maxLength(即底线的长度)除以每一行的元素数量来得到块宽度。然后把元素放在每个块的中间。

参数minWidth表示底部行中块的长度。

用一张图片来说明想法并展示结果。