108. Convert Sorted Array to Binary Search Tree.cpp

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












/**
 * 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:

    void convert(vector<int> &nums, int start, int end, TreeNode* &root){
        if(start > end) return;

        int mid=start+(end-start)/2;
        root=new TreeNode(nums[mid]);

        convert(nums, start, mid-1, root->left);
        convert(nums, mid+1, end, root->right);
    }

    TreeNode* sortedArrayToBST(vector<int>& nums) {
        int n=nums.size();
        TreeNode *root=NULL;
        convert(nums, 0, n-1, root);
        return root;
    }
};