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();
}

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));
    }
}

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。

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   

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