Leetcode147: 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

/** * 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 flatten(TreeNode* root) {        if(!root)            return;        while(root)        {            if(root->left)            {                TreeNode* node = root->left;                while(node->right)                {                    node = node->right;                }                node->right = root->right ;                root->right = root->left;                root->left = NULL;            }            root = root->right;        }    }};