convert-sorted-array-to-binary-search-tree.cpp

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