LeetCode Convert Sorted Array to Binary Search Tree

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

假期回来，水一发

第二轮：

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

写出来一样的代码