941. Valid Mountain Array

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

Recall that A is a mountain array if and only if:

• A.length >= 3
• There exists some i with 0 < i < A.length - 1 such that:
  • A[0] < A[1] < ... A[i-1] < A[i]
  • A[i] > A[i+1] > ... > A[A.length - 1]
判断一个数组是不是山峰数组，就是先严格递增然后严格递减，不能相等

    class Solution(object):
        def validMountainArray(self, A):
            """
            :type A: List[int]
            :rtype: bool
            """
            index = 1
            n = len(A)
            while index < n and A[index] > A[index - 1]:
                index += 1
            if index == 1 or index == n:
                return False
            while index < n and A[index] < A[index - 1]:
                index += 1
            return index == n