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      一次基本操作：root为1，56移动到4下面，2移动到原本5的位置。root变为2

The flattened tree should look like:

   1    \     2      \       3        \         4          \           5            \             6

1、右子树移动到左子树的最右边，然后将左子树移到右子树的位置

2、root往后移，回到步骤1

/** * 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 bianhuan(TreeNode* r1, TreeNode* r2)    {        TreeNode* p = r1;        while (p->right)            p = p->right;        p->right = r2;    }    void flatten(TreeNode* root)     {        if (!root || (!root->left && !root->right))            return;               if (!root->left)            flatten(root->right);        else if(!root->right)        {            root->right = root->left;            root->left = NULL;            flatten(root->right);        }             else        {            bianhuan(root->left,root->right);             root->right=root->left;            root->left=NULL;            flatten(root->right);        }    }};