108. Convert Sorted Array to Binary Search Tree

Description

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

Answer

func help(nums []int, left, right int) *TreeNode {
    if left > right {
        return nil
    }
    idx := int((left + right) / 2)
    root := &TreeNode{
        Val:   nums[idx],
        Left:  nil,
        Right: nil,
    }
    root.Left = help(nums, left, idx-1)
    root.Right = help(nums, idx+1, right)
    return root
}

func sortedArrayToBST(nums []int) *TreeNode {
    return help(nums, 0, len(nums)-1)

}