108. 将有序数组转换为二叉搜索树

递归解法

func sortedArrayToBST(_ nums: [Int]) -> TreeNode? {
    return sortTree(nums, 0, nums.count - 1)
}

func sortTree(_ nums: [Int], _ left: Int, _ right: Int) -> TreeNode? {
    if left > right {
        return nil
    }
    let mid = (left + right) / 2
    let root = TreeNode(nums[mid])
    root.left = sortTree(nums, left, mid - 1)
    root.right = sortTree(nums, mid + 1, right)

    return root
}