896. Monotonic Array

🟩 Easy

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 <= 10^5

• -10^5 <= nums[i] <= 10^5

Solution

My Solution

func isMonotonic(nums []int) bool {
    if len(nums) < 2 {
        return true
    }

    m := 0

    for i:=1; i<len(nums); i++ {
        if nums[i] > nums[i-1] {
            if m == 0 {
                m = 1
            } else if m == -1 {
                return false
            }
        } else if nums[i] < nums[i-1] {
            if m == 0 {
                m = -1
            } else if m == 1 {
                return false
            }
        }
    }

    return true
}

Optimal Solution

func isMonotonic(nums []int) bool {
    isIncreasing, isDecreasing := true, true
    for i := 0; i < len(nums)-1; i++ {
        if nums[i] > nums[i+1] {
            isIncreasing = false
        }
        if nums[i] < nums[i+1] {
            isDecreasing = false
        }
        if !isIncreasing && !isDecreasing {
            return false
        }
    }
    return true
}

result

Leetcode: link