[Leetcode] Convert Sorted List to Binary Search Tree

/**
* 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 *sortedListToBST(ListNode *head) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int cnt = 0;
ListNode* cur = head;
while (cur)
{
cur = cur->next;
cnt++;
}

return build(head, 0, cnt - 1);
}

TreeNode* build(ListNode* &head, int left, int right)
{
if (left > right)
return NULL;

int mid = left + (right - left) / 2;
TreeNode* leftChild = build(head, left, mid - 1);
TreeNode* parent = new TreeNode(head->val);
parent->left = leftChild;
head = head->next;
parent->right = build(head, mid + 1, right);
return parent;
}
};