896. Monotonic Array - Explanation

1. Two Pass

class Solution:
    def isMonotonic(self, nums: List[int]) -> bool:
        n = len(nums)
        increase = True
        for i in range(1, n):
            if nums[i] < nums[i - 1]:
                increase = False
                break

        if increase:
            return True

        decrease = True
        for i in range(1, n):
            if nums[i] > nums[i - 1]:
                decrease = False
                break
        return decrease

Time & Space Complexity

Time complexity: $O(n)$
Space complexity: $O(1)$

2. One Pass - I

class Solution:
    def isMonotonic(self, nums: List[int]) -> bool:
        n = len(nums)
        if nums[0] <= nums[-1]:
            for i in range(1, n):
                if nums[i] < nums[i - 1]:
                    return False
            return True
        else:
            for i in range(1, n):
                if nums[i] > nums[i - 1]:
                    return False
            return True

Time & Space Complexity

Time complexity: $O(n)$
Space complexity: $O(1)$

3. One Pass - II

class Solution:
    def isMonotonic(self, nums: List[int]) -> bool:
        increase, decrease = True, True

        for i in range(len(nums) - 1):
            if not (nums[i] <= nums[i + 1]):
                increase = False
            if not (nums[i] >= nums[i + 1]):
                decrease = False
        return increase or decrease

Time & Space Complexity

Time complexity: $O(n)$
Space complexity: $O(1)$