142 lines
3.9 KiB
PHP
142 lines
3.9 KiB
PHP
<?php declare(strict_types=1);
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function parse_reports(string $file = './input.txt'): array
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{
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$raw = file_get_contents($file);
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$lines = explode("\n", trim($raw));
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return array_map(fn (string $line) => explode(' ', $line), $lines);
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}
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class Report {
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public function __construct(
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public array $rawLevels,
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public array $safeLevels = [],
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private bool $allIncreasing = true,
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private bool $allDecreasing = true,
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private bool $safeDifference = true,
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) {
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$this->rawLevels = array_map(fn ($item) => (int)$item, $this->rawLevels);
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$this->calculateLevelSafety();
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}
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public function isSafe(): bool
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{
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return $this->safeDifference && ($this->allIncreasing xor $this->allDecreasing);
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}
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public function isSafeWithDampener(): bool
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{
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if ($this->isSafe())
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{
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return true;
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}
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$unsafe = $this->getUnsafeKeys();
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$unsafeCount = count($unsafe);
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foreach ($unsafe as $key)
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{
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$front = array_slice($this->rawLevels, 0, $key);
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$back = array_slice($this->rawLevels, $key + 1);
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$newRawLevels = array_merge($front, $back);
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$newReport = new Report($newRawLevels);
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$isNowSafe = $newReport->isSafe();
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if ($isNowSafe)
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{
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// echo json_encode([
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// 'old' => $this,
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// 'new' => $newReport
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// ], JSON_PRETTY_PRINT);
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return true;
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}
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}
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return false;
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}
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private function getUnsafeKeys(): array
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{
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$out = [];
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foreach ($this->safeLevels as $key => $value)
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{
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if (!$value)
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{
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$out[] = $key;
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}
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}
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return $out;
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}
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private function calculateLevelSafety (): void
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{
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$allIncreasing = true;
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$allDecreasing = true;
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$safeDifference = true;
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$safeLevels = [];
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$safeDiff = function ($curr, $prev): bool {
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$diff = abs($curr - $prev);
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return $diff > 0 && $diff < 4;
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};
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$increasing = fn ($curr, $prev): bool => $curr > $prev;
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$decreasing = fn ($curr, $prev): bool => $curr < $prev;
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for ($i = 1; $i < count($this->rawLevels); $i++)
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{
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$curr = $this->rawLevels[$i];
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$prev = $this->rawLevels[$i - 1];
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$isIncreasing = $increasing($curr, $prev);
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$isDecreasing = $decreasing($curr, $prev);
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$isSafeDiff = $safeDiff($curr, $prev);
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$this->allIncreasing = $this->allIncreasing && $isIncreasing;
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$this->allDecreasing = $this->allDecreasing && $isDecreasing;
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$this->safeDifference = $this->safeDifference && $isSafeDiff;
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$safeLevel = $isSafeDiff && (
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$this->allIncreasing xor
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$this->allDecreasing
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);
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$this->safeLevels[] = $safeLevel;
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}
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}
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}
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// ----------------------------------------------------------------------------
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$testReports = array_map(fn (array $line) => new Report($line), parse_reports('./test_input.txt'));
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$testSafeReports = array_filter($testReports, fn (Report $r) => $r->isSafe());
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$testSafeReportsMap = array_map(fn (Report $r) => $r->isSafe(), $testReports);
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assert($testSafeReportsMap == [true, false, false, false, false, true]);
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assert(count($testSafeReports)==2, 'First example has 2 safe reports');
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$testSafeReportsPart2 = array_filter($testReports, fn (Report $r) => $r->isSafeWithDampener());
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$testSafeReportsPart2Map = array_map(fn (Report $r) => $r->isSafeWithDampener(), $testReports);
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assert($testSafeReportsPart2Map == [true, false, false, true, true, true]);
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assert(count($testSafeReportsPart2)==4);
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// ----------------------------------------------------------------------------
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$reports = array_map(fn (array $line) => new Report($line), parse_reports());
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$safeReports = array_filter($reports, fn (Report $r) => $r->isSafe());
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$simpleSafeReports = count($safeReports);
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$allSafeReports = array_filter($reports, fn (Report $r) => $r->isSafeWithDampener());
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$dampenedSafeReports = count($allSafeReports);
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$maybeValid = $dampenedSafeReports > 550
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&& $dampenedSafeReports != 557
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&& $dampenedSafeReports < 572;
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echo "(Part 1) Number of safe reports: $simpleSafeReports\n";
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echo "(Part 2) Number of safe reports with dampener: $dampenedSafeReports\n";
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echo "Part two may be valid: " . $maybeValid . "\n";
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