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

  class Solution {
public:
    void flatten(TreeNode* root) {
        if(!root) return ;
        if(root->left) //不要漏

        {flatten(root->left);
        TreeNode *p=root->left,*q=root->left;
        while(p->right) p=p->right;

        p->right=root->right;
        root->right=q;
        root->left=NULL;}
        flatten(root->right);//不要漏


    }
};