0941-valid-mountain-array.py

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        if len(arr) < 3:
            return False
        peak = valley = 0
        for i in range(1, len(arr) - 1):
            if arr[i-1] < arr[i] > arr[i+1]:
                peak += 1
            if arr[i-1] >= arr[i] <= arr[i+1]:
                valley += 1
        return peak == 1 and valley == 0