[LeetCode] 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.

这题的关键是能找出当前链表的中间节点，然后再递归左右的子链表，开始的时候程序先计算链表总厂，然后传入两个前后索引指针，最后每次递归找出中间节点即可。

 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     int calLen(ListNode *node)
21     {
22         int len = 0;
23         while(node)
24         {
25             len++;
26             node = node->next;
27         }
28         return len;
29     }
30     
31     TreeNode *createTree(ListNode *node, int left, int right)
32     {
33         if (left > right)
34             return NULL;
35             
36         int mid = (left + right) / 2;
37         
38         ListNode *p = node;
39         
40         for(int i = left; i < mid; i++)
41             p = p->next;
42             
43         TreeNode *leftNode = createTree(node, left, mid - 1);
44         TreeNode *rightNode = createTree(p->next, mid + 1, right);
45         
46         TreeNode *tNode = new TreeNode(p->val);
47         
48         tNode->left = leftNode;
49         tNode->right = rightNode;
50         
51         return tNode;        
52     }
53     
54     TreeNode *sortedListToBST(ListNode *head) {
55         // Start typing your C/C++ solution below
56         // DO NOT write int main() function
57         int len = calLen(head);
58         return createTree(head, 0, len - 1);
59     }
60 };

 

 

posted @ 2012-10-29 15:20  chkkch  阅读(4020)  评论(2)  编辑  收藏  举报