Write a method named isMonotonic that accepts an array of integers as a parameter and returns true if the array's element values are monotonic; that is, whether the array is entirely in ascending or descending order.
For example, if an array called a stores {2, 5, 7, 18} or {9, 6, 2, 2, 0, -4}, then the call of isMonotonic(a) should return true.
If the array not in monotonic order, such as {4, 8, 7, 11, 12}, return false.
An empty, one-element, or two-element array is always considered to be monotonic.
An optimal solution runs in O(N) time and uses a constant amount of extra space.
You should not modify the contents of the array passed to your method.
