108. Convert Sorted Array to Binary Search Tree

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

Accepted

315,779

Submissions

589,391

 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return build(nums,0,nums.size()-1);
    }
    
    TreeNode* build(vector<int> &num, int l, int r)
    {
        if(l>r)return NULL;
        int m=(l+r)/2;
        TreeNode *p=new TreeNode(num[m]);
        p->left=build(num,l,m-1);
        p->right=build(num,m+1,r);
        return p;
    }
};