如何打印二叉树图？

Question

如何打印二叉树图？

如何在Java中打印二叉树，以便输出如下：

   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;

    }

}

Answer 1

我已经创建了简单的二叉树打印机。您可以根据需要使用和修改它，但无论如何它都没有进行优化。我认为这里可以改进很多东西;）import&nbsp;java.util.ArrayList;import&nbsp;java.util.Collections;import&nbsp;java.util.List;public&nbsp;class&nbsp;BTreePrinterTest&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;Node<Integer>&nbsp;test1()&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;root&nbsp;=&nbsp;new&nbsp;Node<Integer>(2); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n11&nbsp;=&nbsp;new&nbsp;Node<Integer>(7); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n12&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n21&nbsp;=&nbsp;new&nbsp;Node<Integer>(2); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n22&nbsp;=&nbsp;new&nbsp;Node<Integer>(6); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n23&nbsp;=&nbsp;new&nbsp;Node<Integer>(3); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n24&nbsp;=&nbsp;new&nbsp;Node<Integer>(6); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n31&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n32&nbsp;=&nbsp;new&nbsp;Node<Integer>(8); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n33&nbsp;=&nbsp;new&nbsp;Node<Integer>(4); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n34&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n35&nbsp;=&nbsp;new&nbsp;Node<Integer>(8); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n36&nbsp;=&nbsp;new&nbsp;Node<Integer>(4); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n37&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n38&nbsp;=&nbsp;new&nbsp;Node<Integer>(8); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;root.left&nbsp;=&nbsp;n11; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;root.right&nbsp;=&nbsp;n12; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n11.left&nbsp;=&nbsp;n21; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n11.right&nbsp;=&nbsp;n22; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n12.left&nbsp;=&nbsp;n23; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n12.right&nbsp;=&nbsp;n24; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n21.left&nbsp;=&nbsp;n31; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n21.right&nbsp;=&nbsp;n32; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n22.left&nbsp;=&nbsp;n33; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n22.right&nbsp;=&nbsp;n34; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n23.left&nbsp;=&nbsp;n35; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n23.right&nbsp;=&nbsp;n36; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n24.left&nbsp;=&nbsp;n37; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n24.right&nbsp;=&nbsp;n38; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;root; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;Node<Integer>&nbsp;test2()&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;root&nbsp;=&nbsp;new&nbsp;Node<Integer>(2); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n11&nbsp;=&nbsp;new&nbsp;Node<Integer>(7); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n12&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n21&nbsp;=&nbsp;new&nbsp;Node<Integer>(2); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n22&nbsp;=&nbsp;new&nbsp;Node<Integer>(6); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n23&nbsp;=&nbsp;new&nbsp;Node<Integer>(9); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n31&nbsp;=&nbsp;new&nbsp;Node<Integer>(5); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n32&nbsp;=&nbsp;new&nbsp;Node<Integer>(8); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Node<Integer>&nbsp;n33&nbsp;=&nbsp;new&nbsp;Node<Integer>(4); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;root.left&nbsp;=&nbsp;n11; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;root.right&nbsp;=&nbsp;n12; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n11.left&nbsp;=&nbsp;n21; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n11.right&nbsp;=&nbsp;n22; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n12.right&nbsp;=&nbsp;n23; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n22.left&nbsp;=&nbsp;n31; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n22.right&nbsp;=&nbsp;n32; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;n23.left&nbsp;=&nbsp;n33; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;root; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;static&nbsp;void&nbsp;main(String[]&nbsp;args)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printNode(test1()); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printNode(test2()); &nbsp;&nbsp;&nbsp;&nbsp;}}class&nbsp;Node<T&nbsp;extends&nbsp;Comparable<?>>&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;Node<T>&nbsp;left,&nbsp;right; &nbsp;&nbsp;&nbsp;&nbsp;T&nbsp;data; &nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;Node(T&nbsp;data)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.data&nbsp;=&nbsp;data; &nbsp;&nbsp;&nbsp;&nbsp;}}class&nbsp;BTreePrinter&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;static&nbsp;<T&nbsp;extends&nbsp;Comparable<?>>&nbsp;void&nbsp;printNode(Node<T>&nbsp;root)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;maxLevel&nbsp;=&nbsp;BTreePrinter.maxLevel(root); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printNodeInternal(Collections.singletonList(root),&nbsp;1,&nbsp;maxLevel); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;<T&nbsp;extends&nbsp;Comparable<?>>&nbsp;void&nbsp;printNodeInternal(List<Node<T>>&nbsp;nodes,&nbsp;int&nbsp;level,&nbsp;int&nbsp;maxLevel)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(nodes.isEmpty()&nbsp;||&nbsp;BTreePrinter.isAllElementsNull(nodes)) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;floor&nbsp;=&nbsp;maxLevel&nbsp;-&nbsp;level; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;endgeLines&nbsp;=&nbsp;(int)&nbsp;Math.pow(2,&nbsp;(Math.max(floor&nbsp;-&nbsp;1,&nbsp;0))); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;firstSpaces&nbsp;=&nbsp;(int)&nbsp;Math.pow(2,&nbsp;(floor))&nbsp;-&nbsp;1; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;betweenSpaces&nbsp;=&nbsp;(int)&nbsp;Math.pow(2,&nbsp;(floor&nbsp;+&nbsp;1))&nbsp;-&nbsp;1; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(firstSpaces); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;List<Node<T>>&nbsp;newNodes&nbsp;=&nbsp;new&nbsp;ArrayList<Node<T>>(); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(Node<T>&nbsp;node&nbsp;:&nbsp;nodes)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(node&nbsp;!=&nbsp;null)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.print(node.data); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;newNodes.add(node.left); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;newNodes.add(node.right); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;else&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;newNodes.add(null); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;newNodes.add(null); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.print("&nbsp;"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(betweenSpaces); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(""); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;i&nbsp;=&nbsp;1;&nbsp;i&nbsp;<=&nbsp;endgeLines;&nbsp;i++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;j&nbsp;=&nbsp;0;&nbsp;j&nbsp;<&nbsp;nodes.size();&nbsp;j++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(firstSpaces&nbsp;-&nbsp;i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(nodes.get(j)&nbsp;==&nbsp;null)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(endgeLines&nbsp;+&nbsp;endgeLines&nbsp;+&nbsp;i&nbsp;+&nbsp;1); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;continue; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(nodes.get(j).left&nbsp;!=&nbsp;null) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.print("/"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(1); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(i&nbsp;+&nbsp;i&nbsp;-&nbsp;1); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(nodes.get(j).right&nbsp;!=&nbsp;null) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.print("\\"); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(1); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BTreePrinter.printWhitespaces(endgeLines&nbsp;+&nbsp;endgeLines&nbsp;-&nbsp;i); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(""); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;printNodeInternal(newNodes,&nbsp;level&nbsp;+&nbsp;1,&nbsp;maxLevel); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;void&nbsp;printWhitespaces(int&nbsp;count)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;i&nbsp;=&nbsp;0;&nbsp;i&nbsp;<&nbsp;count;&nbsp;i++) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.print("&nbsp;"); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;<T&nbsp;extends&nbsp;Comparable<?>>&nbsp;int&nbsp;maxLevel(Node<T>&nbsp;node)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(node&nbsp;==&nbsp;null) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;0; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;Math.max(BTreePrinter.maxLevel(node.left),&nbsp;BTreePrinter.maxLevel(node.right))&nbsp;+&nbsp;1; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;private&nbsp;static&nbsp;<T>&nbsp;boolean&nbsp;isAllElementsNull(List<T>&nbsp;list)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(Object&nbsp;object&nbsp;:&nbsp;list)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(object&nbsp;!=&nbsp;null) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;false; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;true; &nbsp;&nbsp;&nbsp;&nbsp;}}输出1：&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;2&nbsp;&nbsp;&nbsp;6&nbsp;&nbsp;&nbsp;3&nbsp;&nbsp;&nbsp;6&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;/&nbsp;\&nbsp;/&nbsp;\&nbsp;/&nbsp;\&nbsp;/&nbsp;\&nbsp; &nbsp;&nbsp;5&nbsp;8&nbsp;4&nbsp;5&nbsp;8&nbsp;4&nbsp;5&nbsp;8输出2：&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;7&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp; &nbsp;/&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\&nbsp;&nbsp; &nbsp;2&nbsp;&nbsp;&nbsp;6&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;9&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;\&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;5&nbsp;8&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4

Answer 2

我为此做了一个改进的算法，它可以很好地处理不同大小的节点。它使用线条自上而下打印。package alg;import java.util.ArrayList;import java.util.List;/**&nbsp;* Binary tree printer&nbsp;*&nbsp;&nbsp;* @author MightyPork&nbsp;*/public class TreePrinter{&nbsp; &nbsp; /** Node that can be printed */&nbsp; &nbsp; public interface PrintableNode&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; /** Get left child */&nbsp; &nbsp; &nbsp; &nbsp; PrintableNode getLeft();&nbsp; &nbsp; &nbsp; &nbsp; /** Get right child */&nbsp; &nbsp; &nbsp; &nbsp; PrintableNode getRight();&nbsp; &nbsp; &nbsp; &nbsp; /** Get text to be printed */&nbsp; &nbsp; &nbsp; &nbsp; String getText();&nbsp; &nbsp; }&nbsp; &nbsp; /**&nbsp; &nbsp; &nbsp;* Print a tree&nbsp; &nbsp; &nbsp;*&nbsp;&nbsp; &nbsp; &nbsp;* @param root&nbsp; &nbsp; &nbsp;*&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; tree root node&nbsp; &nbsp; &nbsp;*/&nbsp; &nbsp; public static void print(PrintableNode root)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; List<List<String>> lines = new ArrayList<List<String>>();&nbsp; &nbsp; &nbsp; &nbsp; List<PrintableNode> level = new ArrayList<PrintableNode>();&nbsp; &nbsp; &nbsp; &nbsp; List<PrintableNode> next = new ArrayList<PrintableNode>();&nbsp; &nbsp; &nbsp; &nbsp; level.add(root);&nbsp; &nbsp; &nbsp; &nbsp; int nn = 1;&nbsp; &nbsp; &nbsp; &nbsp; int widest = 0;&nbsp; &nbsp; &nbsp; &nbsp; while (nn != 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; List<String> line = new ArrayList<String>();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; nn = 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (PrintableNode n : level) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (n == null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; line.add(null);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next.add(null);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next.add(null);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String aa = n.getText();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; line.add(aa);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (aa.length() > widest) widest = aa.length();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next.add(n.getLeft());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next.add(n.getRight());&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (n.getLeft() != null) nn++;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (n.getRight() != null) nn++;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (widest % 2 == 1) widest++;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lines.add(line);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; List<PrintableNode> tmp = level;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; level = next;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next = tmp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next.clear();&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; int perpiece = lines.get(lines.size() - 1).size() * (widest + 4);&nbsp; &nbsp; &nbsp; &nbsp; for (int i = 0; i < lines.size(); i++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; List<String> line = lines.get(i);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int hpw = (int) Math.floor(perpiece / 2f) - 1;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (i > 0) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int j = 0; j < line.size(); j++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // split node&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; char c = ' ';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (j % 2 == 1) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (line.get(j - 1) != null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; c = (line.get(j) != null) ? '┴' : '┘';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (j < line.size() && line.get(j) != null) c = '└';&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(c);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // lines and spaces&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (line.get(j) == null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int k = 0; k < perpiece - 1; k++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(" ");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int k = 0; k < hpw; k++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(j % 2 == 0 ? " " : "─");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(j % 2 == 0 ? "┌" : "┐");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int k = 0; k < hpw; k++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(j % 2 == 0 ? "─" : " ");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.println();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // print line of numbers&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int j = 0; j < line.size(); j++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String f = line.get(j);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (f == null) f = "";&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int gap1 = (int) Math.ceil(perpiece / 2f - f.length() / 2f);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int gap2 = (int) Math.floor(perpiece / 2f - f.length() / 2f);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // a number&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int k = 0; k < gap1; k++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(" ");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(f);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int k = 0; k < gap2; k++) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.print(" ");&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; System.out.println();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; perpiece /= 2;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}要将它用于您的树，请让您的Node类实现PrintableNode。示例输出：&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;2952:0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ┌───────────────────────┴───────────────────────┐&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;1249:-1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;5866:0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; ┌───────────┴───────────┐&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;┌───────────┴───────────┐&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp;491:-1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 1572:0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 4786:1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 6190:0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; ┌─────┘&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;└─────┐&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;┌─────┴─────┐&nbsp; &nbsp; &nbsp;339:0&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 5717:0&nbsp; &nbsp; &nbsp; 6061:0&nbsp; &nbsp; &nbsp; 6271:0&nbsp; &nbsp;