I like that sort of problems. If only to construct recursive algorithms for them.
Here is a recursive procedure to construct and print out all paths of given length from a last visited node, provided a head path is already given and we know what nodes are left for a potential visit:
use strict;
use warnings;
my %adj = (
1 => [2,5,6],
2 => [1,3,5,6,7],
3 => [2,4,6,7,8],
4 => [3,7,8],
5 => [1,2,6,9,10],
6 => [1,2,3,5,7,9,10,11],
7 => [2,3,4,6,8,10,11,12],
8 => [3,4,7,11,12],
9 => [5,6,10,13,14],
10 => [5,6,7,9,11,13,14,15],
11 => [6,7,8,10,12,14,15,16],
12 => [7,8,11,15,16],
13 => [9,10,14],
14 => [9,10,11,13,15],
15 => [10,11,12,14,16],
16 => [11,12,15]
);
sub boggle {
my ($sofar, $last, $remains, $lentogo) = @_;
return print "@$sofar\n" unless $lentogo;
return () unless @$remains;
my (@right, @left) = @$remains;
while (my $next = shift @right) {
boggle([@$sofar, $next], $next, [@left, @right], $lentogo-1) i
+f grep {$next==$_} @{$adj{$last}};
push(@left, $next);
}
}
for my $len (3 .. 6) { # len 3 .. 6
for my $start (1 .. 16) { # all starting points
boggle([$start],$start,[1..$start-1,$start+1..16], $len);
}
};
the last lines show the application to print out all paths of lengths 3 .. 6 starting anywhere on the 16 grid points.
Edit: fixed a bug in the while loop.
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