Problem

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

Code

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
static int var = [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return func(nums);
    }
    TreeNode* func(vector<int> nums){
        if(nums.empty())
            return NULL;
        int mid = nums.size()/2;
        TreeNode* root = new TreeNode(nums[mid]);
        vector<int> left_temp(nums.begin(),nums.begin()+mid);
        root->left = func(left_temp);
        vector<int> right_temp(nums.begin()+mid+1,nums.end());
        root->right = func(right_temp);
        return root;
    }
};

Result

108. Convert Sorted Array to Binary Search Tree.png