我如何在Java中打印一个二叉树,这样输出就像:

   4 
  / \ 
 2   5 

我的节点:

public class Node<A extends Comparable> {
    Node<A> left, right;
    A data;

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

当前回答

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:

其他回答

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:

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   
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   

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:

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。