Convert Sorted Array to Binary Search Tree （递增数组建高度平衡的二叉查找树）【leetcode】

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

顺序给了，求一个高度平衡的二叉查找树。

递归去划分并维护子树在数组中的范围。

/**
 * 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 *sortedArrayToBST(vector<int> &num) {
        return build(num,0,num.size()-1);
    }
    
    TreeNode *build(vector<int> &num,int left,int right)
    {
        if(left>right)return NULL;
        int mid=left+(right-left)/2;
        TreeNode *root=new TreeNode(num[mid]);
        root->left=build(num,left,mid-1);
        root->right=build(num,mid+1,right);
        return root;
    }
};