941. Valid Mountain Array.py

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)