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.

解题思路：找到链表的中点，作为根，前端作为左子树，后端作为右子树，并对前后做递归操作。

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode *getbTree(ListNode *head,int start,int end)
{
if(start<=end)
{
int mid = (start+end)>>1;
ListNode *work = head;
ListNode *rstart=NULL;
for(int i=start;i<mid;i++)
{
work = work->next;
}
rstart = work->next;
TreeNode *node = new TreeNode(work->val);
node->left = getbTree(head,start,mid-1);
node->right = getbTree(rstart,mid+1,end);
return node;
}
else
return NULL;
}
TreeNode *sortedListToBST(ListNode *head) {
if(head==NULL)return NULL;
int len = 0;
ListNode *p = head;
while(p)
{
++len;
p=p->next;
}

return getbTree(head,0,len-1);

}
};