LeetCode:Invert Binary Tree

Invert Binary Tree

Total Accepted: 92036  Total Submissions: 200903  Difficulty: Easy

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.

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c++ code:

/**
 * 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(NULL == root) return NULL;
        
        root->left = invertTree(root->left);
        root->right = invertTree(root->right);
        TreeNode *t = root->left;
        root->left = root->right;
        root->right = t;
        
        return root;
    }
};