896. Monotonic Array.java

/*
An array is monotonic if it is either monotone increasing or monotone decreasing.
An array A is monotone increasing if for all i <= j, A[i] <= A[j].
An array A is monotone decreasing if for all i <= j, A[i] >= A[j].
Return true if and only if the given array A is monotonic.

Example 1:

Input: [1,2,2,3]
Output: true
Example 2:

Input: [6,5,4,4]
Output: true
Example 3:

Input: [1,3,2]
Output: false
Example 4:

Input: [1,2,4,5]
Output: true
Example 5:

Input: [1,1,1]
Output: true
*/

// My really not great whiteboard answer
class Solution {
	public boolean isMonotonic(int[] A) {
		int prev = A[0];
		int i = 1;

		if (A.length == 1)
			return true;
		while (A[i] == prev) {
			i++;
		if (i == A.length)
			return true;
		}

		if (A[i] < prev) {
			for (int j = i; j < A.length; j++) {
				if (A[j] > prev)
					return false;
				prev = A[j];
			}
		} else {
			for (int k = i; k < A.length; k++) {
				if (A[k] < prev)
					return false;
				prev = A[k];
			}
		}
		return true;
	}
}