https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
平衡二叉树,使用递归将右边和左边的节点再输出平衡二叉树

func sortedArrayToBST(_ nums: [Int]) -> TreeNode? {
	guard !nums.isEmpty else { return nil }
	guard nums.count > 1 else { return TreeNode(nums[0]) }
	let mid = nums.count/2
	let root = TreeNode(nums[mid])
	root.left = sortedArrayToBST(Array(nums[0..<mid]))
	root.right = sortedArrayToBST(Array(nums[mid+1..<nums.count]))
	return root
}

A013EC17-3734-4770-9424-0EBC32DBD8BF