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:

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

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。

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   

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);

    }
}

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();
}