LeetCode OJ

题目：

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

The flattened tree should look like:

Hints:

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

解题思路：

依照前序遍历二叉树的方法进行处理。

代码：

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     void pre_order(TreeNode * root) {
13         if (root == NULL) return;
14 
15         if (root->left != NULL)    pre_order(root->left);
16         if (root->right != NULL) pre_order(root->right);
17 
18         if (root->left != NULL) {
19             TreeNode *cur = root->left;
20             while (cur->right != NULL) {
21                 cur = cur->right;
22             }
23             cur->right = root->right;
24             root->right = root->left;
25             root->left = NULL;
26         }
27         return;
28     }
29     void flatten(TreeNode *root) {
30         pre_order(root);
31     }
32 };