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leetcode - Convert Sorted List to Binary Search Tree

2013-03-28 10:23  张汉生  阅读(114)  评论(0)  编辑  收藏  举报

题目描述：点击此处

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 /**
10  * Definition for binary tree
11  * struct TreeNode {
12  *     int val;
13  *     TreeNode *left;
14  *     TreeNode *right;
15  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
16  * };
17  */
18 class Solution {
19 public:
20     TreeNode *sortedListToBST(ListNode *head) {
21         // Start typing your C/C++ solution below
22         // DO NOT write int main() function
23       if (head==NULL)
24         return NULL;
25       int size = 0;
26       ListNode * middle = head;
27       while (middle != NULL){
28         size++;
29         middle = middle->next;
30       }
31       size /= 2;
32       ListNode * last = NULL;
33       middle = head;
34       while (size>0){
35         last = middle;
36         middle = middle->next;
37         size--;
38       }
39       TreeNode * root = new TreeNode(middle->val);
40       if (middle != head){
41         last->next = NULL;
42         root->left = sortedListToBST(head);
43       }
44       root->right = sortedListToBST(middle->next);
45       return root;
46     }
47 };