58 lines
1.4 KiB
PHP
58 lines
1.4 KiB
PHP
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<?php
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$input_file = '../inputs/day10.txt';
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if (file_exists($input_file)) {
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$input = file_get_contents($input_file);
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if ($input != null) {
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$joltages = array_map('trim', explode("\n", $input));
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print 'Part 1 answer: ' . solve_part_one($joltages) . "\n";
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print 'Part 2 answer: ' . solve_part_two($joltages) . "\n";
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}
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}
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function solve_part_one(array $joltages): int
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{
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$sorted_joltages = $joltages;
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$sorted_joltages[] = "0";
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sort($sorted_joltages);
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$sorted_joltages[] = $sorted_joltages[count($sorted_joltages) - 1] + 3;
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$differences = chain_adapters($sorted_joltages);
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return $differences[0] * $differences[2];
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}
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function solve_part_two(array $joltages): int
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{
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$sorted_joltages = $joltages;
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$sorted_joltages[] = "0";
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sort($sorted_joltages);
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$sorted_joltages[] = $sorted_joltages[count($sorted_joltages) - 1] + 3;
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return get_max_chains($sorted_joltages);
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}
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function chain_adapters(array $joltages): array
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{
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$differences = [0, 0, 0];
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for ($i = 1; $i < count($joltages); $i++) {
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$diff = $joltages[$i] - $joltages[$i - 1];
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$differences[$diff - 1] += 1;
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}
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return $differences;
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}
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function get_max_chains(array $joltages): int
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{
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$jolt_count = count($joltages);
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$memo = [$jolt_count - 1 => 1];
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for ($i = $jolt_count - 2; $i >= 0; $i--) {
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$count = 0;
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for ($j = $i + 1; $j < $jolt_count && $joltages[$j] - $joltages[$i] <= 3; $j++) {
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$count += $memo[$j];
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}
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$memo[$i] = $count;
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}
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return $memo[0];
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}
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