[Tutor] longest common substring

[lina]

Hi,

I tested the one from
http://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Longest_common_substring

mainly:

#!/usr/bin/python3

a=['1','2','3','7']

b=['2','3','7']

def LongestCommonSubstring(S1, S2):
        M = [[0]*(1+len(S2)) for i in range(1+len(S1))]
        longest, x_longest = 0, 0
        for x in range(1,1+len(S1)):
                for y in range(1,1+len(S2)):
                        M[x][y] = M[x-1][y-1]+1
                        if M[x][y] > longest:
                                longest = M[x][y]
                                x_longest = x
                        else:
                                M[x][y] = 0
        return S1[x_longest-longest:x_longest]


if __name__=="__main__":
        print(LongestCommonSubstring(a,b))

$ python3 LongestCommonSubstring.py
['1', '2', '3']

The results isn't right.

Thanks for your suggestions and comments,

Best regards,