leetcode-109. Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

 

思路：才用快慢指针，找到中间节点，然后递归处理。

accepted code：

 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 a binary tree node.
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         if(head==nullptr)
22         return nullptr;
23         return toBST(head,nullptr);
24     }
25     
26     TreeNode* toBST(ListNode* head,ListNode* end)
27     {
28         ListNode* slow=head;
29         ListNode* fast=head;
30         if(head==end)
31         return nullptr;
32         
33         while(fast!=end&&fast->next!=end)
34         {
35             fast=fast->next->next;
36             slow=slow->next;
37         }
38         
39         TreeNode* root=new TreeNode(slow->val);
40         root->left=toBST(head,slow);
41         root->right=toBST(slow->next,end);
42         return root;
43     }
44 };

 

posted @ 2017-02-20 13:56  Pacific-hong  阅读(113)  评论(0)  编辑  收藏  举报