72 lines
1.9 KiB
PHP
72 lines
1.9 KiB
PHP
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<?php
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$instructions = explode("\n", file_get_contents('input.txt'));
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$acc = 0;
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$used_indexes = [];
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$current_index = 0;
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$to_change = [];
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// find all nop and jmp indexes
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foreach ($instructions as $index => $instruction) {
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if (in_array(substr($instruction, 0, 3), ['nop', 'jmp'])) {
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$to_change[] = $index;
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}
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}
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// copy instructions
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$original_instructions = $instructions;
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while (true) {
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if (!array_key_exists($current_index, $instructions)) {
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echo $acc;
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exit;
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}
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if (in_array($current_index, $used_indexes, true)) {
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// fail, reset and change next nop or jmp
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$acc = 0;
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$used_indexes = [];
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$current_index = 0;
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$instructions = $original_instructions;
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$changed_instruction_index = array_shift($to_change);
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$instruction_to_change = $instructions[$changed_instruction_index];
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[$command, $math] = explode(' ', $instruction_to_change);
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if ($command === 'nop') {
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$instructions[$changed_instruction_index] = sprintf('jmp %s', $math);
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} else {
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$instructions[$changed_instruction_index] = sprintf('nop %s', $math);
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}
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continue;
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}
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$used_indexes[] = $current_index;
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$current_op = $instructions[$current_index];
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[$command, $value] = explode(' ', $current_op);
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if ($command === 'nop') {
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$current_index++;
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continue;
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}
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$math_op = $value[0];
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$math_value = substr($value, 1);
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if ($command === 'acc') {
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if ($math_op === '+') {
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$acc += (int)$math_value;
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} else {
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$acc -= (int)$math_value;
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}
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$current_index++;
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continue;
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}
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if ($command === 'jmp') {
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if ($math_op === '+') {
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$current_index += (int)$math_value;
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} else {
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$current_index -= (int)$math_value;
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}
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continue;
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}
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}
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