Determining the monotonicity of a numerical array

You are given an array of integers. Implement a function that returns true if the array is strictly or non-strictly monotonically increasing, or strictly or non-strictly monotonically decreasing. In other cases, the function should return false.

def is_monotonic(nums: List[int]) -> bool:
    # implement monotonicity check
    pass

public static boolean isMonotonic(int[] numbers) {
    // implement monotonicity check
    return false;
}

bool isMonotonic(const std::vector<int>& arr) {
    // implement monotonicity check
    return false;
}