【leetcode】941. Valid Mountain Array

题目如下：

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[B.length - 1]

Example 1:

Input: [2,1]
Output: false

Example 2:

Input: [3,5,5]
Output: false

Example 3:

Input: [0,3,2,1]
Output: true

Note:

1. 0 <= A.length <= 10000
2. 0 <= A[i] <= 10000 

解题思路：非常简单的题目，没啥说的。

代码如下：

class Solution(object):
    def validMountainArray(self, A):
        """
        :type A: List[int]
        :rtype: bool
        """
        if len(A) < 3:
            return False
        last = None
        directon = None
        for i in A:
            if last == None:
                last = i
            elif directon == None and last < i:
                directon = 0
                last = i
            elif directon == None and last > i:
                return False
            elif directon == 0 and last < i:
                last = i
            elif directon == 0 and last > i:
                directon = 1
                last = i
            elif directon == 1 and last > i:
                last = i
            else:
                return False
        return directon == 1