Challenge 2, recursion time

1 files changed, 33 insertions, 0 deletions

diff --git a/challenge-100/simon-proctor/raku/ch-2.raku b/challenge-100/simon-proctor/raku/ch-2.raku
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+++ b/challenge-100/simon-proctor/raku/ch-2.raku
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+#!/usr/bin/env raku
+
+use v6;
+
+#! Given a series of comma seperated number lists making a triangle (1 -> 2 -> 3 digits long)
+#! find the path down the triangle that adds up to the least amount
+multi sub MAIN( *@input ) {
+    my @lines = @input.map( *.split(",") );
+    die "Not a triangle" unless [==] 1, |(@lines.map( *.elems ).rotor(2=>-1).map( { @^a[1] - @^a[0] } ) );
+    say smallest-route( @lines );
+}
+
+multi sub MAIN("test") {
+    use Test;
+    is( 8, smallest-route( [ [1], [2,4], [6,4,9], [5,1,7,2] ] ) );
+    is( 7, smallest-route( [ [3], [3,1], [5,2,3], [4,3,1,3] ] ) );
+}
+
+multi sub smallest-route( @start ) {
+    return smallest-route( @start[0], @start[1..*-1], 0 );    
+}
+
+multi sub smallest-route( @head, [], $index ) {
+    return @head[$index];
+}
+
+multi sub smallest-route( @head, @rest, $index ) {
+    my @opts = [
+        smallest-route( @rest[0], @rest[1..*-1], $index ),
+        smallest-route( @rest[0], @rest[1..*-1], $index+1 )
+    ];
+    return @head[$index] + (@opts[0] < @opts[1] ?? @opts[0] !! @opts[1]);
+}