day 3

public/days/Day3.php

@@ -0,0 +1,58 @@
+<?php
+
+final class Day3 extends Day {
+
+	function part1(): string {
+		$matches = [];
+		$input = implode("", $this->input);
+		preg_match_all("/mul\(([0-9]{1,3}),([0-9]{1,3})\)/", $input, $matches, PREG_SET_ORDER);
+
+		$sum = 0;
+
+		/** @var array<string> $match */
+		foreach ($matches as $match) {
+			$factor1 = intval($match[1]);
+			$factor2 = intval($match[2]);
+
+			$sum += $factor1 * $factor2;
+		}
+
+		return intval($sum);
+	}
+
+	function part2(): string {
+		$input = implode("", $this->input);
+
+		$mulMatches = [];
+		preg_match_all("/mul\(([0-9]{1,3}),([0-9]{1,3})\)/", $input, $mulMatches, PREG_SET_ORDER | PREG_OFFSET_CAPTURE);
+
+		$doMatches = [];
+		preg_match_all("/do\(\)|don't\(\)/", $input, $doMatches, PREG_OFFSET_CAPTURE);
+		$doMatches = $doMatches[0];
+
+		$sum = 0;
+		$enabled = true;
+
+		$nextDoInstructionIndex = 0;
+
+		/** @var array<array> $match */
+		foreach ($mulMatches as $match) {
+			$position = intval($match[0][1]);
+
+			$nextDoInstruction = $doMatches[$nextDoInstructionIndex] ?? null;
+			if ($nextDoInstruction && $position > $nextDoInstruction[1]){
+				$enabled = $nextDoInstruction[0] === 'do()';
+				$nextDoInstructionIndex++;
+			}
+
+			if ($enabled){
+				$factor1 = intval($match[1][0]);
+				$factor2 = intval($match[2][0]);
+
+				$sum += $factor1 * $factor2;
+			}
+		}
+
+		return intval($sum);
+	}
+}