AdventOfCode2024/public/days/Day1.php

<?php

final class Day1 extends Day {

	function part1(): string {
		$left = [];
		$right = [];

		foreach ($this->input as $line){
			[$left[], $right[]] = array_map("intval", explode("   ", $line));
		}

		sort($left);
		sort($right);

		$sum = 0;

		for ($i = 0; $i < count($left); $i++){
			$sum += abs($left[$i] - $right[$i]);
		}

		return strval($sum);
	}

	function part2(): string {
		$left = [];
		$rightCounts = [];

		foreach ($this->input as $line){
			[$left[], $right] = array_map("intval", explode("   ", $line));
			if (array_key_exists($right, $rightCounts)){
				$rightCounts[$right]++;
			} else {
				$rightCounts[$right] = 1;
			}
		}

		$sum = 0;

		foreach ($left as $number){
			$sum += $number * ($rightCounts[$number] ?? 0);
		}

		return strval($sum);
	}
}