1 files changed, 57 insertions, 0 deletions
diff --git a/2020/day3.raku b/2020/day3.raku
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+++ b/2020/day3.raku
@@ -0,0 +1,57 @@
+#!/usr/bin/env raku
+
+use v6;
+
+constant \EXAMPLE = q:to/END/;
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#
+END
+
+sub solve($input, Int $step-right, Int $step-down --> Int) {
+    # Parse it
+    my @m = $input.split("\n").grep(*.chars > 0).map(*.comb.Array);
+    my $x = 0;
+    my $y = 0;
+    my $trees = 0;
+    my $width = @m[0].elems;
+
+    while $y < @m.elems {
+        $trees++ if @m[$y][$x] eq '#';
+
+        $y += $step-down;
+        $x = ($x + $step-right) % $width;
+    }
+    $trees
+}
+
+multi sub MAIN('part1', $file) {
+    say solve(slurp($file), 3, 1);
+}
+
+multi sub MAIN('part2', $file) {
+    my $input = slurp $file;
+    my &f = &solve.assuming($input);
+    say (
+        f(1, 1),
+        f(3, 1),
+        f(5, 1),
+        f(7, 1),
+        f(1, 2)
+    ).reduce: &[*]
+}
+
+multi sub MAIN('test') {
+    use Test;
+    subtest 'Part 1', {
+        is solve(EXAMPLE, 3, 1), 7, 'Example';
+    }
+}