109 lines
2.3 KiB
PHP
109 lines
2.3 KiB
PHP
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<?php
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use JetBrains\PhpStorm\Pure;
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$input_file = '../inputs/day8.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$instructions = 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 $instructions): int
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{
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return get_acc(parse_instructions($instructions));
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}
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function solve_part_two(array $instructions): int
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{
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$original_instructions = parse_instructions($instructions);
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foreach ($original_instructions as $idx => $instruction) {
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$altered_instructions = $original_instructions;
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switch ($instruction[0]) {
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case 'jmp':
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$altered_instructions[$idx][0] = 'nop';
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break;
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case 'nop':
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$altered_instructions[$idx][0] = 'jmp';
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break;
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}
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if (terminates_correctly($altered_instructions))
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return get_acc($altered_instructions);
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}
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return 0;
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}
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#[Pure] function terminates_correctly(array $instructions): bool
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{
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$acc = 0;
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$ip = 0;
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$execution_count = [];
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while ($ip < count($instructions)) {
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if (array_key_exists($ip, $execution_count) && $execution_count[$ip] != 0)
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return false;
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$execution_count[$ip] = 1;
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[$acc, $ip] = run_instruction($instructions[$ip], [$acc, $ip]);
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}
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return true;
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}
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#[Pure] function get_acc(array $instructions): int
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{
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$acc = 0;
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$ip = 0;
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$execution_count = [];
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while ($ip < count($instructions)) {
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if (array_key_exists($ip, $execution_count) && $execution_count[$ip] != 0)
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return $acc;
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$execution_count[$ip] = 1;
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[$acc, $ip] = run_instruction($instructions[$ip], [$acc, $ip]);
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}
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return $acc;
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}
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function run_instruction(array $instruction, array $regs): array
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{
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[$inst, $arg] = $instruction;
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[$acc, $ip] = $regs;
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switch ($inst) {
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case 'acc':
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$acc += $arg;
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$ip += 1;
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break;
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case 'jmp':
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$ip += $arg;
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break;
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case 'nop':
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$ip += 1;
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break;
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}
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// print 'Executed ' . $inst . ', $acc = ' . $acc . ', $ip = ' . $ip . "\n";
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return [$acc, $ip];
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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 $instruction) {
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if (preg_match('/^(acc|jmp|nop) ([+\-\d]+)$/', trim($instruction), $matches)) {
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[, $inst, $arg] = $matches;
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$parsed_instructions[] = [$inst, $arg];
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}
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}
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return $parsed_instructions;
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}
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