leetcode: 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

递归，规律就是先把根的右指针指向左子树，左子树的最右儿子指向原来根的右儿子

/**
* 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;
flatten( root->left);
flatten( root->right);
if( root->left == NULL){
return;
}
TreeNode *tmp = root->left;
TreeNode *tmp2 = root->right;
root->left = NULL;
root->right = tmp;
while( tmp->right)
tmp = tmp->right;
tmp->right = tmp2;
}
};