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题目：
Invert a binary tree.
4 / 2 7 / \ / 1 3 6 9
to
4 / 7 2 / \ / 9 6 3 1
Trivia:
This problem was inspired by this original tweet by Max Howell:
Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.
题意：反转一个二叉树，加点题外话，很简单的一个题，不过有关于这道题的小故事，点击链接即可。
思路1：利用递归
代码：
public class Solution { public TreeNode invertTree(TreeNode root) { if(root == null || (root.left == null && root.right == null)) return root; TreeNode temp = root.right; root.right = invertTree(root.left); root.left = invertTree(temp); return root; } }
思路2：非递归，利用stack
代码2：
public class Solution { public TreeNode invertTree(TreeNode root) { if(root == null) return null; Stack<TreeNode> stack = new Stack<TreeNode>(); stack.push(root); while(!stack.isEmpty()){ TreeNode cur = stack.pop(); TreeNode temp = cur.left; cur.left = cur.right; cur.right = temp; if(cur.left != null) stack.push(cur.left); if(cur.right != null) stack.push(cur.right); } return root; } }
[LeetCode-JAVA] Invert Binary Tree
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原文地址：http://www.cnblogs.com/TinyBobo/p/4590425.html
