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### Re: puzzle: how many ways to make \$100 (with Prolog!)

by Ovid (Cardinal)
 on Apr 29, 2006 at 04:00 UTC ( #546463=note: print w/replies, xml ) Need Help??

in reply to puzzle: how many ways to make \$100

Well, if you're serious about teaching her logic skills ;) (I've ignored two dollar bills for simplicity. It should be trivial to add it)

```#!/usr/bin/perl

use strict;
use warnings;
use AI::Prolog;

my @bills = qw(Fifties Twenties Tens Fives Ones);
my \$bills = join ',', @bills; # don't use \$prolog->list because these
+are vars

my \$program = <<"END_PROLOG";
change([ \$bills ]) :-
member(Fifties,[0,1,2]),
member(Twenties,[0,1,2,3,4,5]),
member(Tens,[0,1,2,3,4,5,6,7,8,9,10]),
member(Fives,[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20
+]),
Total is 50*Fifties + 20*Twenties +10*Tens + 5*Fives,
Total <= 100,
Ones is 100 - Total.

member(X, [X|_]).
member(X, [_|Tail]) :-
member(X, Tail).
END_PROLOG

my \$prolog = AI::Prolog->new(\$program);
\$prolog->query("change([ \$bills ]).");
while (my \$result = \$prolog->results) {
for my \$i ( 0 .. \$#bills ) {
print "\$result->[1][\$i] \$bills[\$i]";
print ", " unless \$i == \$#bills;
}
print "\n";
}
__END__
# Beginning of output:
0 Fifties, 0 Twenties, 0 Tens, 0 Fives, 100 Ones
0 Fifties, 0 Twenties, 0 Tens, 1 Fives, 95 Ones
0 Fifties, 0 Twenties, 0 Tens, 2 Fives, 90 Ones
0 Fifties, 0 Twenties, 0 Tens, 3 Fives, 85 Ones
0 Fifties, 0 Twenties, 0 Tens, 4 Fives, 80 Ones
0 Fifties, 0 Twenties, 0 Tens, 5 Fives, 75 Ones
0 Fifties, 0 Twenties, 0 Tens, 6 Fives, 70 Ones
0 Fifties, 0 Twenties, 0 Tens, 7 Fives, 65 Ones
0 Fifties, 0 Twenties, 0 Tens, 8 Fives, 60 Ones
...

Cheers,
Ovid

New address of my CGI Course.

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