0941-Valid-Mountain-Array.py

'''
Given an array of integers arr, return true if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:
arr.length >= 3
There exists some i with 0 < i < arr.length - 1 such that:
arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
arr[i] > arr[i + 1] > ... > arr[arr.length - 1]


Example 1:
Input: arr = [2,1]
Output: false

Example 2:
Input: arr = [3,5,5]
Output: false

Example 3:
Input: arr = [0,3,2,1]
Output: true
 
Constraints:
1 <= arr.length <= 104
0 <= arr[i] <= 104
'''

from typing import List

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        if len(arr) < 3:
            return False
        i = 1
        while i < len(arr) and arr[i] > arr[i-1]:
            i += 1
        if i == 1 or i == len(arr):
            return False
        while i < len(arr) and arr[i] < arr[i-1]:
            i += 1
        return i == len(arr)

s = Solution()
answer = s.validMountainArray([1, 2, 3, 2, 1]) # True
print(answer)
answer = s.validMountainArray([1, 2, 2, 4, 1, 5]) # False
print(answer)