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.

好吧，还是用递归！

/**
* 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 *buildTree(ListNode *&head, int begin, int end) {
if(begin > end) return NULL;
int mid = (begin + end) / 2;
TreeNode *root = new TreeNode(0);
root->left = buildTree(head, begin, mid - 1);
root->val = head->val;
head = head->next;
root->right = buildTree(head, mid + 1, end);
return root;
}

TreeNode *sortedListToBST(ListNode *head) {
ListNode *temp = head;
int length = 0;
while(temp != NULL) {
length ++;
temp = temp->next;
}
return buildTree(head, 0, length - 1);
}
};