LeetCode 114. Flatten Binary Tree to Linked List

 1 class Solution {
 2 public:
 3     void flatten(TreeNode* root) {
 4         if(!root) return;
 5         flatten(root->left);
 6         flatten(root->right);
 7         
 8         TreeNode* right = root->right;
 9         root->right = root->left;
10         root->left = NULL;
11         while(root->right){
12             root = root->right;
13         }
14         root->left = NULL;
15         root->right = right;
16     }
17 };