Invert a binary tree.
to4 / 2 7 / \ / 1 3 6 9
Trivia:4 / 7 2 / \ / 9 6 3 1
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.
反转一个二叉树，使用递归很容易就可以实现。递归交换节点即可。
class Solution { public: TreeNode* invertTree(TreeNode* root) { if (root == nullptr) return 0; root->left = invertTree(root->left); root->right = invertTree(root->right); swap(root->left, root->right); return root; } }; // 0 ms
使用迭代实现
class Solution { public: TreeNode* invertTree(TreeNode* root) { if (root == nullptr) return 0; stack<TreeNode*> s; s.push(root); while (!s.empty()) { TreeNode* node = s.top(); s.pop(); if (node->left != nullptr) s.push(node->left); if (node->right != nullptr) s.push(node->right); swap(node->left, node->right); } return root; } }; // 0 ms
[LeetCode] Construct String from Binary Tree
原文：http://www.cnblogs.com/immjc/p/7152418.html