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

思路: 首先找到根节点左节点的最右子节点，然后把根节点的右子树移到左子树的最右端；接着把根结点的左子树移到右节点上，并将左子树置为空树，同时将根结点往右下移一个节点，依次递归即可。代码如下：

Code(c++):

/**
 * 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 && root->right){
                TreeNode *p = root->left;
                while(p->right) 
                    p =p->right;
                p->right = root->right;
            }


            if(root->left)
                root->right = root->left;
            root->left = NULL;
            root = root->right;
        }
    }
};