896 Monotonic Array - Easy

Problem:

An array is monotonic if it is either monotone increasing or monotone decreasing.

An array nums is monotone increasing if for all i <= j, nums[i] <= nums[j]. An array nums is monotone decreasing if for all i <= j, nums[i] >= nums[j].

Given an integer array nums, return true if the given array is monotonic, or false otherwise.

Example 1:

Input: nums = [1,2,2,3] Output: true

Example 2:

Input: nums = [6,5,4,4] Output: true

Example 3:

Input: nums = [1,3,2] Output: false

Constraints:

• 1 <= nums.length <= 105
• -105 <= nums[i] <= 105

Problem Analysis:

• On first thought, one may consider performing 2 loops through the list; the first to check for increasing, the second for decreasing
• we can initialize 2 flags and check for both condition in one go.
• Time complexity: O(n)

Solutions:

class Solution:
    def isMonotonic(self, nums: List[int]) -> bool:
        increasing, decreasing = True, True
        for i in range(len(nums)-1):
            if nums[i] > nums[i+1]:
                decreasing = False
            elif nums[i] < nums[i+1]:
                increasing = False
        return increasing or decreasing

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