108. Convert Sorted Array to Binary Search Tree.cpp

// 108. Convert Sorted Array to Binary Search Tree
// Solved
// Easy
// Topics
// Companies
// Given an integer array nums where the elements are sorted in ascending order, convert it to a 
// height-balanced
//  binary search tree.

 

// Example 1:


// Input: nums = [-10,-3,0,5,9]
// Output: [0,-3,9,-10,null,5]
// Explanation: [0,-10,5,null,-3,null,9] is also accepted:

// Example 2:


// Input: nums = [1,3]
// Output: [3,1]
// Explanation: [1,null,3] and [3,1] are both height-balanced BSTs.
 

// Constraints:

// 1 <= nums.length <= 104

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return sortedArrayToBSTHelper(nums, 0, nums.size()-1);
    }
private:
    TreeNode* sortedArrayToBSTHelper(const vector<int>& nums, int start, int end) {
        if(start>end){
            return nullptr;
        }
        int mid=start+(end-start)/2;
        TreeNode* root=new TreeNode(nums[mid]);
        root->left=sortedArrayToBSTHelper(nums,start,mid-1);
        root->right=sortedArrayToBSTHelper(nums,mid+1,end);
        return root;
    }
};