Task 2 done

1 files changed, 31 insertions, 0 deletions

diff --git a/challenge-147/luca-ferrari/raku/ch-2.p6 b/challenge-147/luca-ferrari/raku/ch-2.p6
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+++ b/challenge-147/luca-ferrari/raku/ch-2.p6
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+#!raku
+
+ sub MAIN( Int $limit = 3000 ) {
+
+     my ( %pentagons, %inverse-pentagons );
+     %pentagons{ $_ } = ( $_ * ( 3 * $_ - 1 ) / 2 ) for 1 .. $limit;
+     %inverse-pentagons{ %pentagons{ $_ } } = $_ for %pentagons.keys.sort;
+
+
+
+     for %pentagons.keys.sort -> $index-left {
+         for %pentagons.keys.sort -> $index-right {
+             next if $index-left == $index-right;
+
+
+             my ( $sum, $diff ) = %pentagons{ $index-left } + %pentagons{ $index-right },
+                                                            abs( %pentagons{ $index-left } - %pentagons{ $index-right } );
+
+             # this is too slow, therefore I use an inverse hash!
+             # next if ! %pentagons.values.grep( * ~~ $sum );
+             # next if ! %pentagons.values.grep( * ~~ $diff );
+             next if %inverse-pentagons{ $diff }:!exists;
+             next if %inverse-pentagons{ $sum }:!exists;
+
+             "P( $index-left ) + P( $index-right ) = { %pentagons{ $index-left } } + { %pentagons{ $index-right } } = $sum = P( { %inverse-pentagons{ $sum } } )".say;
+             "P( $index-left ) - P( $index-right ) = { %pentagons{ $index-left } } + { %pentagons{ $index-right } } = $diff = P( {%inverse-pentagons{ $diff } } )".say;
+             exit;
+         }
+     }
+
+ }