896 Monotonic Array.py

#!/usr/bin/python3
"""
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


Note:

1 <= A.length <= 50000
-100000 <= A[i] <= 100000
"""
from typing import List


class Solution:
    def isMonotonic(self, A: List[int]) -> bool:
        mono = 0  # 0 undecided, 1 decr, 2 incr
        for i in range(1, len(A)):
            if mono == 0:
                if A[i] > A[i-1]:
                    mono = 2
                elif A[i] < A[i-1]:
                    mono = 1
            else:
                if A[i] > A[i-1] and mono == 1:
                    return False
                elif A[i] < A[i-1] and mono == 2:
                    return False
        else:
            return True