AdventOfCode2024/public/days/Day3.php

<?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);
	}
}