90 lines
2.2 KiB
PHP
90 lines
2.2 KiB
PHP
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<?php
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$input_file = '../inputs/day14.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$instructions = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($instructions) . "\n";
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print 'Part 2 answer: ' . solve_part_two($instructions) . "\n";
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}
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}
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function solve_part_one(array $instructions): int
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{
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$parsed = parse_instructions($instructions);
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$mask = '';
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$mem = [];
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foreach ($parsed as $instruction) {
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if ($instruction[0] === 'mask')
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$mask = $instruction[1];
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else
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$mem[$instruction[1]] = apply_mask($mask, $instruction[2]);
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}
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return array_sum($mem);
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}
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function solve_part_two(array $instructions): int
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{
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$parsed = parse_instructions($instructions);
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$mask = '';
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$mem = [];
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foreach ($parsed as $instruction) {
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if ($instruction[0] === 'mask')
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$mask = $instruction[1];
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else {
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foreach (apply_mask_two($mask, $instruction[1]) as $address)
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$mem[$address] = $instruction[2];
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}
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}
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return array_sum($mem);
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}
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function apply_mask_two(string $mask, int $num): array
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{
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$addresses = [''];
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$bin = str_pad(decbin($num), 36, '0', STR_PAD_LEFT);
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for ($i = 0; $i < strlen($bin); $i++) {
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switch ($mask[$i]) {
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case '0':
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$addresses = array_map(fn ($addr) => $addr . $bin[$i], $addresses);
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break;
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case '1':
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$addresses = array_map(fn ($addr) => $addr . '1', $addresses);
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break;
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case 'X':
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$new_addresses = [];
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foreach ($addresses as $address) {
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$new_addresses[] = $address . '0';
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$new_addresses[] = $address . '1';
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}
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$addresses = $new_addresses;
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break;
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}
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}
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return array_map('bindec', $addresses);
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}
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function apply_mask(string $mask, int $num): int
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{
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$bin = str_pad(decbin($num), 36, '0', STR_PAD_LEFT);
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for ($i = 0; $i < strlen($bin); $i++)
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if ($mask[$i] != 'X')
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$bin[$i] = $mask[$i];
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return bindec($bin);
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}
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function parse_instructions(array $instructions): array
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{
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$parsed_instructions = [];
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foreach ($instructions as $instruction) {
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[$inst, $arg] = array_map('trim', explode(' = ', $instruction));
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if ($inst === 'mask')
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$parsed_instructions[] = [$inst, $arg];
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else
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$parsed_instructions[] = ['mem', substr($inst, 4, strlen($inst) - 5), $arg];
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}
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return $parsed_instructions;
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}
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