Given an array, return true if it is monotone increasing or monotone decreasing.
Example 1:
Input: nums = [1, 2, 2, 3]
Output: true
Explanation: The array is monotone increasing.
Example 2:
Input: nums = [6, 5, 4, 4]
Output: true
Explanation: The array is monotone decreasing.
Example 3:
Input: nums = [1, 3, 2]
Output: false