AdventOfCode2024/public/days/Day2.php

<?php

final class Day2 extends Day {

	function part1(): string {
		$safeCount = 0;

		foreach ($this->input as $line){
			$levels = array_map('intval', explode(' ', $line));

			$isSafe = true;


			$direction = null;
			for ($i = 0; $i < count($levels) - 1; $i++){
				$levelNow = $levels[$i];
				$levelThen = $levels[$i + 1];

				$change = abs($levelThen - $levelNow);
				if ($change < 1 || $change > 3){
					$isSafe = false;
					break;
				}

				if ($direction === null){
					$direction = $levelThen > $levelNow;
				}

				if ($direction !== ($levelThen > $levelNow)){
					$isSafe = false;
					break;
				}
			}

			if ($isSafe)
				$safeCount++;
		}

		return strval($safeCount);
	}

	function part2(): string {
		$safeCount = 0;

		foreach ($this->input as $line){
			$levels = array_map('intval', explode(' ', $line));

			$isSafe = false;

			for ($removeLevelIndex = -1; $removeLevelIndex < count($levels); $removeLevelIndex++){
				$localLevels = $levels;
				if ($removeLevelIndex > -1){
					array_splice($localLevels, $removeLevelIndex, 1);
				}

				$levelSetIsSafe = true;
				$direction = null;
				for ($i = 0; $i < count($localLevels) - 1; $i++){
					$levelNow = $localLevels[$i];
					$levelThen = $localLevels[$i + 1];

					$change = abs($levelThen - $levelNow);
					if ($change < 1 || $change > 3){
						$levelSetIsSafe = false;
						break;
					}

					if ($direction === null){
						$direction = $levelThen > $levelNow;
					}

					if ($direction !== ($levelThen > $levelNow)){
						$levelSetIsSafe = false;
						break;
					}
				}
				if ($levelSetIsSafe){
					$isSafe = true;
					break;
				}
			}

			if ($isSafe)
				$safeCount++;


		}

		return strval($safeCount);
	}
}