From 8fadbab611b74777d020c4cc18ab2b13776c40c1 Mon Sep 17 00:00:00 2001
From: Guillermo Ramos
Date: Thu, 30 May 2019 22:12:23 +0200
Subject: [010#2]

---
 010/ch2.pl | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100755 010/ch2.pl

diff --git a/010/ch2.pl b/010/ch2.pl
new file mode 100755
index 0000000..9e72fad
--- /dev/null
+++ b/010/ch2.pl
@@ -0,0 +1,60 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+use List::Util qw<max min>;
+
+sub jaro {
+	my @s1 = split //, shift;
+	my @s2 = split //, shift;
+
+	# Two chars in s1 and s2 match if they are not farther away than this number
+	my $match_dist = int(max (scalar @s1, scalar @s2) / 2)-1;
+	$match_dist = 0 if $match_dist < 0;
+
+	# Maps indices from s1 chars to matching s2 chars
+	my %matches;
+
+	# Compute matches (fill the %matches hash)
+	S1:
+	foreach my $i (0 .. $#s1) {
+		foreach my $j ($i-min($i, $match_dist) .. min($i+$match_dist, $#s2)) {
+			# Skip s2 char if already matched
+			next if grep(/$j/, values %matches);
+
+			# If characters match, store match and advance to next char in s1
+			if ($s1[$i] eq $s2[$j]) {
+				$matches{$i} = $j;
+				next S1;
+			}
+		}
+	}
+
+	# Count number of matches and exit if 0
+	my $m = keys %matches;
+	return 0 if $m == 0;
+
+	# Count transpositions
+	my $t = 0;
+	for my $k (keys %matches) {
+		$t += 1 if $k != $matches{$k};
+	}
+
+	# Finally compute and return Jaro distance
+	return (($m/@s1) + ($m/@s2) + (($m-$t)/$m))/3;
+}
+
+sub jaro_winkler {
+	my ($s1, $s2) = @_;
+	my $jarosim = jaro $s1, $s2;
+	my $l;
+	for ($l = 0; $l < length $s1; $l++) {
+		last if (substr($s1, $l, 1) ne (substr $s2, $l, 1));
+	}
+	my $p = 0.1;
+	return $jarosim + $l*$p*(1-$jarosim);
+}
+
+die "Usage: $0 <s1> <s2>" unless @ARGV == 2;
+print jaro_winkler(@ARGV), "\n";
-- 
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