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.

递归，二分法。

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