之字形打印
package com.tll.test; import java.util.LinkedList; import java.util.List; public class Tes { private static class BinaryTreeNode { private int val; private BinaryTreeNode left; private BinaryTreeNode right; public BinaryTreeNode() { } public BinaryTreeNode(int val) { this.val = val; } @Override public String toString() { return val + ""; } } public static void print(BinaryTreeNode root) { if (root == null) { return; } List<BinaryTreeNode> current = new LinkedList<BinaryTreeNode>(); List<BinaryTreeNode> reverse = new LinkedList<BinaryTreeNode>(); int flag = 0; BinaryTreeNode node; current.add(root); while (current.size() > 0) { // 从最后一个开始取 node = current.remove(current.size() - 1); System.out.printf("%-3d", node.val); // 当前是从左往右打印的,那就按从左往右入栈 if (flag == 0) { if (node.left != null) { reverse.add(node.left); } if (node.right != null) { reverse.add(node.right); } } // 当前是从右往左打印的,那就按从右往左入栈 else { if (node.right != null) { reverse.add(node.right); } if (node.left != null) { reverse.add(node.left); } } if (current.size() == 0) { flag = 1 - flag; List<BinaryTreeNode> tmp = current; current = reverse; reverse = tmp; System.out.println(); } } } public static void main(String[] args) { BinaryTreeNode n1 = new BinaryTreeNode(1); BinaryTreeNode n2 = new BinaryTreeNode(2); BinaryTreeNode n3 = new BinaryTreeNode(3); BinaryTreeNode n4 = new BinaryTreeNode(4); BinaryTreeNode n5 = new BinaryTreeNode(5); BinaryTreeNode n6 = new BinaryTreeNode(6); BinaryTreeNode n7 = new BinaryTreeNode(7); BinaryTreeNode n8 = new BinaryTreeNode(8); BinaryTreeNode n9 = new BinaryTreeNode(9); n1.left = n2; n1.right = n3; n2.left = n4; n2.right = n5; n3.left = n6; n3.right = n7; n4.left = n8; n4.right = n9; print(n1); } }