Problem statement

https://leetcode.com/problems/monotonic-array/

Solution

Just check what is asked in O(n) time and O(1) space. We can do two passes or one pass and do early stopping if needed.

Complexity

Time is O(n), space is O(1).

Code

class Solution:
    def isMonotonic(self, A):
        inc = dec = True

        for i in range(len(A) - 1):
            #if not inc and not dec: return False
            if A[i] > A[i+1]: inc = False
            if A[i] < A[i+1]: dec = False

        return inc or dec