40 lines
1.1 KiB
PHP
40 lines
1.1 KiB
PHP
<?php
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$lines = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
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$mapings = [];
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$before = [];
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$initialMappings = [];
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$template = array_shift($lines);
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for ($i = 0; $i < strlen($template) - 1; $i++) {
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$pair = substr($template, $i, 2);
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$before[$pair] = 1;
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}
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foreach ($lines as $item) {
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$line = explode(' -> ', $item);
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$mapings[$line[0]] = $line[1];
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$initialMappings[$line[0]] = 0;
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}
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for ($step = 1; $step <= 40; $step++) {
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$after = $initialMappings;
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foreach ($before as $pair => $count) {
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$left = $pair[0] . $mapings[$pair];
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$right = $mapings[$pair] . $pair[1];
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$after[$left] += $count;
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$after[$right] += $count;
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}
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$before = $after;
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}
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$letters = [];
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foreach ($before as $pair => $count) {
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$left = $pair[0];
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if (!isset($letters[$left])) {
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$letters[$left] = 0;
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}
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$letters[$left] += $count;
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}
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$letters[substr($template, -1)] += 1;
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sort($letters);
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echo array_pop($letters) - array_shift($letters); //2516901104210
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