如何在列表中找到特定模式？

Question

Given a list of numbers containing either 0's, 1's, or -1's, how can I find the longest portion of the list that starts with a +1 and ends with a -1.

For example, [0,0,1,1,1,-1,-1,-1,0] : The longest portion is 6 due to the portion of the list [1,1,1,-1,-1,-1].

For example, [1,-1,0,1,-1,-1,-1] : The longest portion is 4 due to the portion of the list [1,-1,-1,-1]. Note that had the original list only been the first 3 elements (eg, [1,-1,0]), then the correct answer would have been 2 [1,-1].

Also, the list cannot be broken with a 0 and it can only alternate from +1 to -1 once. In other words [+1,-1,+1,-1] is still only 2.

Thank you

Answer 1

You need has two bool(previous_has_one exist, previous_has_neg_one) to record them exist or not.

def getLongestPortion(l):
    maxx = 0
    curMax = 0
    JustHadOne = False
    JustHadNeg = False
    for i in range(len(l)):
        if(l[i]==1):
            if(JustHadNeg):
                curMax = 0
            curMax += 1
            JustHadOne = True
            JustHadNeg = False
        elif(l[i]==-1 and JustHadOne):
            curMax += 1
            maxx = max(maxx,curMax)
            JustHadNeg = True
        else:
            JustHadOne = False
            JustHadNeg = False
            curMax=0
    return maxx

l = [1,-1,-1,0,1,1,-1,-1]
print(getLongestPortion(l))

Answer 2

Here's a regex solution. First I change a list like [1, -1, 0, 1, -1, -1, -1] to a string like 'ab abbb' , then I search for 'a+b+' , then take the maximum length of the matches:

import re

max(map(len, re.findall('a+b+', ''.join(' ab'[i] for i in l))))