29- Monotonic Array

The problem can be found at the following link: Question Link

My Approach

1. Initialize two boolean flags, increasing and decreasing, to true. These flags will help us track whether the array is non-increasing or non-decreasing, respectively.

2. Iterate through the array nums starting from index 1 (comparing each element with the previous one).

3. For each pair of adjacent elements, check whether nums[i] is greater than nums[i - 1]. If it is, set the decreasing flag to false because this indicates that the array is not decreasing.

4. If nums[i] is less than nums[i - 1], set the increasing flag to false because this indicates that the array is not increasing.

5. Continue this process for the entire array.

6. After the loop, check whether either increasing or decreasing is true. If either of them is true, it means that the array is monotonic (either non-increasing or non-decreasing), so return true. Otherwise, return false.

Time and Auxiliary Space Complexity

• Time Complexity: O(n)

• Auxiliary Space Complexity: O(1)

Code (C++)

class Solution {
public:
    bool isMonotonic(vector<int>& nums) {
        bool increasing = true;
        bool decreasing = true;

        for (int i = 1; i < nums.size(); i++) {
            if (nums[i] > nums[i - 1]) {
                decreasing = false;
            } else if (nums[i] < nums[i - 1]) {
                increasing = false;
            }
        }

        return increasing || decreasing;
    }
};

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