class Solution:
def validMountainArray(self, arr: List[int]) -> bool:
peak = 0
n = len(arr)
# Climb to the peak
for i in range(1, n):
if arr[i] > arr[i - 1]:
peak = i
else:
break
# Climb to the peak
# - peak == 0: the starting point is the peak
# - peak == n - 1: the ending point is the peak
if peak == 0 or peak == n - 1:
return False
# Keep climbing to the end
for i in range(peak, n - 1):
# if next point is larger then current point, it goes up again.
if arr[i] <= arr[i + 1]:
return False
return True
