[Tutor] longest common substring

[lina]

On Fri, Nov 11, 2011 at 1:23 AM, Walter Prins <wprins at gmail.com> wrote:
> Hi,
>
> On 10 November 2011 16:23, lina <lina.lastname at gmail.com> wrote:
>>
>> 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]
>
> This is not the same as the implementation given on wikibooks.... Have you
> tried reverting your changes and using the coe that was given on the site
> exactly as is?  (I assume not, and if so, why not?)
I used python3, it showed me NameError: name 'xrange' is not defined
so I made a little changes, before I even worried I might forget to
import some modules to make the xrange work.
>
> (Specifically, I notice most the likely culprit is a missing if statement
> just below the "for y in range..." line that's been deleted....)
Thanks for that. adding this missing line, works. I am still lack of
understanding how the code works, so made above mistake.
>
>>
>> The results isn't right.
>
> Yes.  You appear to have introduced a bug by not using the same code as what
> was given on the wiki page.  (Why did you modify the code and then when the
> modified code didn't work assume the original solution was broken instead of
> checking first and/or suspecting that your changes may have broken it?)
Sorry. I did not assume the original code was broken, might a little
unconsciously worry it might be out of date at that time.
I checked by eyes, bad, and did not check carefully.

Thanks with best regards,


>
> Walte
>
>
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