#Leetcode# 108. Convert Sorted Array to Binary Search Tree

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / 
   -3   9
   /   /
 -10  5

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
	TreeNode * BuildTree(vector<int> &nums, int start, int end)
	{
		if(start >= end)
			return NULL;
		int mid = (start + end)/2;
		TreeNode * cur = new TreeNode(nums[mid]);
		cur ->left = BuildTree(nums, start, mid);
		cur ->right = BuildTree(nums, mid + 1, end);

		return cur;
	}
public:
	TreeNode* sortedArrayToBST(vector<int>& nums) {
        int n = nums.size();
		return BuildTree(nums, 0, n);
	}
};

　　不是很明白为什么是这么写的 本来想的是写一个 $insert$ 函数然后跑 $nums$ 数组但是没写出来 肥去之后再想吧 指针指来指去不是很搞得清