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Re: Longest Common Substring

by BrowserUk (Patriarch)
on Apr 09, 2003 at 20:13 UTC ( #249402=note: print w/replies, xml ) Need Help??


in reply to Longest Common Substring

Enlil's right, my code was a bit slovenly. I believe this is both more correct and more efficient, but I can't guarentee it doesn't fail on some edge case or another.

#! perl -slw use strict; sub lcss (\$\$) { my ($needle, $haystack) = @_; ($needle, $haystack) = ($haystack, $needle) if length $$needle > length $$haystack; my ($longest_c, $longest) = 0; for my $start (0..length $$needle) { for my $len ( reverse $start+1 .. length $$needle) { my $substr = substr($$needle, $start, $len); length $1 > $longest_c and ($longest_c, $longest) = (lengt +h $1, $1) while $$haystack =~ m[($substr)]g; } } return $longest; } my $needle = 'the lazy cat'; my $haystack = 'the quick brown fox jumps over the lazy dog'; print "The longest common substring between\n" , $needle, "\nand\n" , $haystack, "\nis '" , lcss($needle, $haystack) , "'"; $needle = 'i pushed the lazy dog into a creek, the quick brown fox tol +d me to'; $haystack = 'the quick brown fox jumps over the lazy dog'; print "The longest common substring between\n" , $needle, "\nand\n" , $haystack, "\nis '" , lcss($needle, $haystack) , "'"; __END__ C:\test>249239.pl The longest common substring between the lazy cat and the quick brown fox jumps over the lazy dog is 'the lazy ' The longest common substring between i pushed the lazy dog into a creek, the quick brown fox told me to and the quick brown fox jumps over the lazy dog is 'the quick brown fox '

Examine what is said, not who speaks.
1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.

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