75 lines
1.6 KiB
PHP
75 lines
1.6 KiB
PHP
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<?php
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use JetBrains\PhpStorm\Pure;
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$input_file = '../inputs/day9.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$preamble = 25;
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$numbers = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($numbers, $preamble) . "\n";
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print 'Part 2 answer: ' . solve_part_two($numbers, $preamble) . "\n";
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}
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}
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#[Pure] function solve_part_one(array $numbers, int $preamble): int
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{
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return get_first_error($numbers, $preamble);
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}
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function solve_part_two(array $numbers, int $preamble): int
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{
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return get_weakness($numbers, get_first_error($numbers, $preamble));
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}
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function get_first_error(array $numbers, int $preamble): int
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{
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$error = 0;
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for ($i = $preamble; $i < count($numbers); $i++) {
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$correctly_encoded = false;
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for ($j = $i - $preamble; $j < $i; $j++) {
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for ($k = $i - $preamble; $k < $i; $k++) {
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if ($numbers[$j] + $numbers[$k] == $numbers[$i]) {
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$correctly_encoded = true;
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break;
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}
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}
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if ($correctly_encoded)
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break;
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}
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if ($correctly_encoded === false) {
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return $numbers[$i];
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}
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}
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return $error;
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}
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function get_weakness(array $numbers, int $result): int
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{
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$min_pos = 0;
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$length = 2;
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while ($min_pos < count($numbers)) {
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while ($length < count($numbers) - 2) {
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$test = array_slice($numbers, $min_pos, $length);
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if (array_sum($test) == $result) {
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sort($test);
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return $test[0] + $test[count($test) - 1];
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} else if (array_sum($test) > $result) {
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$min_pos += 1;
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$length = 2;
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break;
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}
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$length += 1;
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}
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}
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return 0;
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}
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