Invert a binary tree.

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:
    void revert(TreeNode* node){
        if(NULL != node){
            TreeNode *t = node->left;
            node->left = node->right;
            node->right = t;
            revert(node->left);
            revert(node->right);
        }
    }
    
    TreeNode* invertTree(TreeNode* root) {
        revert(root);
        return root;
    }
};