leetcode/0896_monotonic-array/python3/solution.py

class Solution:
    def isMonotonic(self, nums: List[int]) -> bool:
        # Means difference between two nums indicate that it is
        # decreasing or that difference is 0
        isNonIncreasing = True
        
        # Same idea as above butnopposite: it is either increasing
        # or difference is 0
        isNonDecreasing = True
        
        for i in range(1, len(nums)):
            difference = nums[i] - nums[i - 1]
            
            # We can say with confidence if this condition ever passes
            # that sequence is increasing (e.g. 1 2 4 8 ...)
            if difference > 0:
                isNonIncreasing = False
            # Sequence is decreasing (e.g. 1 0 -2 -4 ...)
            elif difference < 0:
                isNonDecreasing = False
                
            # If both flags are set to False, that means there is no
            # monotonous state and we can break early.
            if not isNonIncreasing and not isNonDecreasing:
                return False
        
        # At the end, if either flag remains True, we have a montonous
        # array
        return isNonIncreasing or isNonDecreasing