60 lines
1.7 KiB
PHP
60 lines
1.7 KiB
PHP
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<?php
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$input_file = '../inputs/day13.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$in = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($in) . "\n";
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print 'Part 2 answer: ' . solve_part_two($in) . "\n";
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}
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}
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function solve_part_one(array $in): int
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{
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[$arrival_time, $lines] = $in;
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$trimmed_bus_lines = array_map('trim', explode(',', $lines));
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$active_lines = array_filter($trimmed_bus_lines, fn ($line) => $line != 'x');
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$bus_arrival_times = array_map(get_closest_arrival_time_to($arrival_time), $active_lines);
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[$min_key] = array_keys($bus_arrival_times, min($bus_arrival_times));
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return $active_lines[$min_key] * ($bus_arrival_times[$min_key] - $arrival_time);
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}
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function solve_part_two(array $in): int
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{
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[, $lines] = $in;
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$trimmed_bus_lines = array_map('trim', explode(',', $lines));
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$active_lines = array_filter($trimmed_bus_lines, fn ($line) => $line != 'x');
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return get_first_consecutive_time($active_lines)[0];
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}
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function get_closest_arrival_time_to(int $target): callable
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{
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return function (int $x) use ($target): int {
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$i = 1;
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while ($i * $x < $target) {
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$i += 1;
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}
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return $i * $x;
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};
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}
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function get_first_consecutive_time(array $lines): array
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{
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if (count($lines) == 1)
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return [0, $lines[0]];
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else {
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$keys = array_keys($lines);
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$last_key = $keys[count($keys) - 1];
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$last_elem = array_pop($lines);
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[$previous_time, $previous_lcm] = get_first_consecutive_time($lines);
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$timestamp = $previous_time;
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while (true) {
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if (($timestamp + $last_key) % $last_elem === 0)
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break;
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else
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$timestamp += $previous_lcm;
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}
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return [$timestamp, $previous_lcm * $last_elem];
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}
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}
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