1 files changed, 52 insertions, 0 deletions
diff --git a/2020/day-09/day-09.raku b/2020/day-09/day-09.raku
new file mode 100755
index 0000000..e9b6683
--- /dev/null
+++ b/2020/day-09/day-09.raku
@@ -0,0 +1,52 @@
+#!/usr/bin/env raku
+
+sub MAIN (
+    Int $part where * == 1|2 = 1 #= part to run (1 or 2)
+) {
+    my @numbers = "input".IO.lines>>.Int;
+    my Int $solution;
+
+    my Int $preamble_length = 25;
+    my Int %invalid;
+
+    MAIN: for @numbers.kv -> $idx, $num {
+        next if $idx < $preamble_length;
+
+        my @preamble = @numbers[$idx - $preamble_length..$idx - 1].sort;
+
+        my Bool $valid;
+        while pop @preamble -> $num_1 {
+            my $diff = $num - $num_1;
+            for @preamble -> $num_2 {
+                if $num_2 == $diff {
+                    $valid = True;
+                    next MAIN;
+                }
+            }
+        }
+
+        unless $valid {
+            %invalid<num> = $num;
+            %invalid<idx> = $idx;
+            $solution = %invalid<num> if $part == 1;
+            last MAIN;
+        }
+    }
+
+    if $part == 2 {
+        my @set = @numbers[0..%invalid<idx> - $preamble_length - 1];
+
+        PART2: for @set.elems - 1 ... 0 -> $idx_1 {
+            for @set.elems - 1 ... 0 -> $idx_2 {
+                my $sum = [+] @set[$idx_1..$idx_2];
+                if $sum == %invalid<num> {
+                    my @tmp = @set[$idx_1..$idx_2].sort;
+                    $solution = @tmp[0] + @tmp[*-1];
+                    last PART2;
+                }
+            }
+        }
+    }
+
+    say "Part $part: ", $solution;
+}