23 lines
665 B
PHP
23 lines
665 B
PHP
<?php
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$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
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$template = array_shift($input);
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$pairs = [];
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foreach ($input as $item) {
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$line = explode(' -> ', $item);
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$pairs[$line[0]] = $line[1];
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}
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$newTemplate = $template;
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for ($j = 0; $j < 10; $j++) {
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$tmpTemplate = $newTemplate;
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for ($i = 0; $i < strlen($tmpTemplate) - 1; $i++) {
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$window = substr($tmpTemplate, $i, 2);
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$newTemplate = substr_replace($newTemplate, $pairs[$window], $i + 1 + $i, 0);
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}
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}
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$characters = array_count_values(str_split(($newTemplate)));
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sort($characters);
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echo array_pop($characters) - array_shift($characters); //2549
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