From 0211c48cce21e17c1fe1026c36f4c8d2108fb96c Mon Sep 17 00:00:00 2001
From: Andinus <andinus@nand.sh>
Date: Tue, 8 Dec 2020 16:49:48 +0530
Subject: Add day-08 solution

---
 2020/day-08/day-08.raku | 88 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100755 2020/day-08/day-08.raku

(limited to '2020/day-08/day-08.raku')

diff --git a/2020/day-08/day-08.raku b/2020/day-08/day-08.raku
new file mode 100755
index 0000000..ee9556f
--- /dev/null
+++ b/2020/day-08/day-08.raku
@@ -0,0 +1,88 @@
+#!/usr/bin/env raku
+
+# Instruction grammar seperates the operation & argument.
+grammar Instruction {
+    rule TOP { <operation> <argument> }
+    token operation { acc|jmp|nop }
+    token argument { .* }
+}
+
+my Int $repeated = 0;
+
+sub MAIN (
+    Int $part where * == 1|2 = 1 #= part to run (1 or 2)
+) {
+    # To match the numbers in instructions with array we just push an
+    # element at 0th index.
+    my @instructions = %(instruction => "", executed => 0),;
+
+    for "input".IO.lines {
+        push @instructions, %(
+            instruction => $_.Str,
+            executed => 0,
+        );
+    }
+
+    my Int $acc;
+    if $part == 1 {
+        $acc = execute-from(@instructions, 1) if $part == 1;
+    } elsif $part == 2 {
+        for @instructions.kv -> $idx, $entry {
+            next if $idx == 0;
+            $repeated = 0;
+            if Instruction.parse($entry<instruction>) -> $match {
+                @instructions[$idx]<instruction> = "nop $match<argument>"
+                if $match<operation> eq "jmp";
+
+                @instructions[$idx]<instruction> = "jmp $match<argument>"
+                if $match<operation> eq "nop";
+
+                $acc = execute-from(@instructions, 1);
+
+                @instructions[$idx]<instruction> = "$match<operation> $match<argument>";
+                @instructions = reset-executed(@instructions);
+
+                last if $repeated == 0;
+            }
+        }
+    }
+    say "Part $part: ", $acc;
+}
+
+sub reset-executed (
+    @instructions is copy --> List
+) {
+    $_<executed> = 0 for @instructions;
+    return @instructions;
+}
+
+# execute-from takes an index & executes instructions from that point.
+# It returns the accumulator value.
+sub execute-from (
+    @instructions, Int $idx --> Int
+) {
+    my Int $acc = 0;
+
+    return $acc unless @instructions[$idx];
+    my $entry = @instructions[$idx];
+
+    $repeated++ if $entry<executed>;
+    return $acc if $entry<executed>;
+
+    if Instruction.parse($entry<instruction>) -> $match {
+        $entry<executed> = 1;
+        given $match<operation> {
+            when 'acc' {
+                $acc += $match<argument>;
+                $acc += execute-from(@instructions, $idx + 1);
+            }
+            when 'jmp' {
+                $acc += execute-from(@instructions, $idx + $match<argument>);
+            }
+            when 'nop' {
+                $acc += execute-from(@instructions, $idx + 1);
+            }
+        }
+    }
+    return $acc;
+}
-- 
cgit 1.4.1-2-gfad0