leetcode 226

1. Invert Binary Tree
   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.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* invertTree(TreeNode* root) {        TreeNode *temp;        if(NULL!=root){            temp=root->left;            root->left=root->right;            root->right=temp;            invertTree(root->left);            invertTree(root->right);        }        return root;    }};