845. Longest Mountain in Array

https://leetcode.com/problems/longest-mountain-in-array/description/

Description

Let's call any (contiguous) subarray B (of A) a mountain if the following properties hold:

B.length >= 3
There exists some 0 < i < B.length - 1 such that B[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1]

(Note that B could be any subarray of A, including the entire array A.)

Given an array A of integers, return the length of the longest mountain.

Return 0 if there is no mountain.

Example 1:
Input: [2,1,4,7,3,2,5]
Output: 5
Explanation: The largest mountain is [1,4,7,3,2] which has length 5.

Example 2:
Input: [2,2,2]
Output: 0
Explanation: There is no mountain.

Note:

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

Follow up:

Can you solve it using only one pass?
Can you solve it in O(1) space?

Solution

class Solution(object):
    def longestMountain(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        if len(A)<=1: return 0
        ret = 0
        pre_foot, pre_top = -1, -1
        for i in range(1, len(A)):
            if A[i]==A[i-1]:
                pre_foot = pre_top = -1
                continue
            if pre_foot==-1:
                if A[i]>A[i-1]: pre_foot = i-1
            elif pre_top==-1:
                if A[i]<A[i-1]:
                    pre_top = i-1
                    ret = max(ret, i-pre_foot+1)
            else:
                if A[i]<A[i-1]:
                    ret = max(ret, i-pre_foot+1)
                else:
                    pre_foot = i-1
                    pre_top = -1
        return ret