[leetCode]Convert Sorted Array to Binary Search Tree

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

构建平衡二叉排序树（AVL）

注意到平衡二叉排序树的根节点是数组的中间点就好，之后是递归。

#include <iostream>
#include <vector>
using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
class Solution {
public:
    TreeNode *sortedArrayToBST(vector<int> &num) {
        TreeNode *head = build(num,0,num.size()-1);
        return head;
    }
    TreeNode *build(vector<int> &num, int low, int high){
        int headnum = (low+high)/2;
        if(low > high) return NULL;
        TreeNode *head = new TreeNode(num[headnum]);
        head->left = build(num, low,headnum-1);
        head->right = build(num,headnum+1,high);
        return head;
    }
};