[leetcode]226. Invert Binary Tree

Invert a binary tree.

Example:

Input:

     4
   /   \
  2     7
 / \   / \
1   3 6   9

Output:

     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 f*** off.

c++代码

/**
 * 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) {
        
        if(root==NULL)
            return NULL;
        if(root->left==NULL && root->right==NULL)
            return root;
        
        TreeNode *temp=root->left;
        root->left=root->right;
        root->right=temp;
        
        if(root->left)
            invertTree(root->left);
                       
        if(root->right)
            invertTree(root->right);
         return root;
        
    }
};