44 lines
1 KiB
PHP
44 lines
1 KiB
PHP
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<?php
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$input_file = '../inputs/day15.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$numbers = array_map('trim', explode(',', $input));
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print 'Part 1 answer: ' . solve_part_one($numbers) . "\n";
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print 'Part 2 answer: ' . solve_part_two($numbers) . "\n";
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}
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}
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function solve_part_one(array $numbers): int
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{
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return get_number_in_sequence($numbers, 2020);
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}
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function solve_part_two(array $numbers): int
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{
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ini_set('memory_limit', '-1');
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return get_number_in_sequence($numbers, 30000000);
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}
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function get_number_in_sequence(array $initial_numbers, int $num): int
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{
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$last_spoken = [];
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foreach ($initial_numbers as $turn => $number)
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$last_spoken[(int)$number] = (int)$turn + 1;
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$last = array_keys($last_spoken)[count($last_spoken) - 1];
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for ($i = count($last_spoken); $i < $num; $i++) {
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if (array_key_exists($last, $last_spoken)) {
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$prev = $last;
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$last = $i - $last_spoken[$last];
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$last_spoken[$prev] = $i;
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} else {
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$last_spoken[$last] = $i;
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$last = 0;
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}
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}
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return $last;
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}
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