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0896 - Monotonic Array (Easy)

Problem Statement​

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 trueif the given array is monotonic, orfalseotherwise.

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

Approach 1: Two Loops​

Written by @wingkwong
class Solution {
public:
    bool isMonotonic(vector<int>& nums) {
        int n = nums.size(), ok = 1;
        // check for monotone increasing
        for (int i = 1 ; i < n; i++) ok &= nums[i - 1] <= nums[i];
        // if it is monotone increasing, return true
        if (ok) return true;
        // reset ok
        ok = 1;
        // check for monotone decreasing
        for (int i = n - 2; i >= 0; i--) ok &= nums[i] >= nums[i + 1];
        // return the answer
        return ok;
    }
};

Approach 2: One Pass​

Written by @wingkwong
class Solution {
public:
    bool isMonotonic(vector<int>& nums) {
        int n = nums.size(), inc = 1, dec = 1;
        for (int i = 1 ; i < n; i++) {
            // check for monotone increasing
            inc &= nums[i - 1] <= nums[i];
            // check for monotone decreasing
            dec &= nums[i - 1] >= nums[i]; 
        }
        // the given is monotonic if either one is true
        return inc || dec;
    }
};