如何在 python 中找到两个字符串之间的最长交集？

Question

I'm trying to write a program that would find the longest intersection between two strings. The conditions are:

1. If there is no common character the program returns an empty chain.
2. If there are multiple substrings of common characters with the same length it should return whichever is the largest, for example, for "bbaacc" and "aabb" the repeating substrings are "aa" and "bb" but as "bb" > "aa", so the programs must return only "bb".
3. Finally the program should return the longest common substring, for instance, for "programme" and "grammaire" the return should be "gramm" not "gramme".

My code has a problem with this last condition, how could I change it so it works as expected?

def intersection(v, w):
    if not v or not w:
        return ""
    x, xs, y, ys = v[0], v[1:], w[0], w[1:]
    if x == y:
        return x + intersection(xs, ys)
    else:
        return max(intersection(v, ys), intersection(xs, w), key=len)

Driver:

print(intersection('programme', 'grammaire'))

Answer 1

cant find the issue with your code, but i solved it like this

def longest_str_intersection(a: str, b: str):

    # identify all possible character sequences from str a
    seqs = []
    for pos1 in range(len(a)):
        for pos2 in range(len(a)):
            seqs.append(a[pos1:pos2+1])
        
    # remove empty sequences
    seqs = [seq for seq in seqs if seq != '']

    # find segments in str b
    max_len_match = 0
    max_match_sequence = ''
    for seq in seqs:
        if seq in b:
            if len(seq) > max_len_match:
                max_len_match = len(seq)
                max_match_sequence = seq

    return max_match_sequence


longest_str_intersection('programme', 'grammaire')
-> 'gramm'

also interested to see if you found a more elegant solution!