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by Sumit Chourasia | Oct 06, 2020 | Category :coding | Tags : algorithm binary-tree data-structure easy leetcode tree

Convert Sorted Array to Binary Search Tree - Tree - Easy - LeetCode

Convert Sorted Array to Binary Search Tree - Tree - Easy - LeetCode

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.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public TreeNode SortedArrayToBST(int[] nums) {        
        var tree = Helper(nums,0,nums.Length-1);
        return tree;
    }
    
    private TreeNode Helper(int[] nums, int start, int end){
        if(start>end){
            return null;
        }
        var tree = new TreeNode();
        int mid = (start+end)/2;
        tree.val = nums[mid];
        tree.left = Helper(nums,start,mid-1);
        tree.right = Helper(nums,mid+1,end);
        return tree;
    }
}

Time Complexity: O(n)

Space Complexity: O(1)

Contributed By: Sumit Chourasia
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