Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1        / \       2   5      / \   \     3   4   6

The flattened tree should look like:

   1    \     2      \       3        \         4          \           5            \             6

Solution Code:

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ typedef vector<int> List; class Solution {public:    void flatten(TreeNode *root) {        if(!root) return;                if(root->left) {            TreeNode *cur = root->left;            while(cur->right) cur = cur->right;            cur->right = root->right;            root->right = root->left;            root->left = NULL;        }                flatten(root->right);    }};