leetcode[114]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 binary tree
 * 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==NULL)return;
    if(root->left)
    {
        TreeNode *pre=root->left;
        while(pre->right)pre=pre->right;
        pre->right=root->right;
        root->right=root->left;
        root->left=NULL;
    }
    flatten(root->right);
}
/*  
    void flatten(TreeNode *root) {
        if(root==NULL)return;
        while(root)
        {
            if(root->left)
            {
                TreeNode *pre=root->left;
                while(pre->right)pre=pre->right;
                pre->right=root->right;
                root->right=root->left;
                root->left=NULL;
            }
            root=root->right;
        }
        return;
  }
*/
};