leetcode 第114题 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

click to show hints.

Hints:

If you notice carefully in the flattened tree, each node’s right child points to the next node of a pre-order traversal.

思路：递归实现。Linked List的结果是二叉树先序遍历的结果。

C++实现：

/**
* 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;
TreeNode *keepright = root->right;
root->right = root->left;
TreeNode *keepleft = root->left;
TreeNode *pre = root;
root->left = NULL;
flatten(keepleft);
while(pre->right != NULL) {
pre = pre->right;
}
pre->right = keepright;
flatten(keepright);
}
};