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<?php declare(strict_types=1); |
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/** |
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* @package s9e\ShortestCommonSuperstring |
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* @copyright Copyright (c) 2016-2019 The s9e authors |
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* @license http://www.opensource.org/licenses/mit-license.php The MIT License |
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*/ |
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namespace s9e\ShortestCommonSuperstring; |
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class ShortestCommonSuperstring |
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{ |
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/** |
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* @var integer Affix length for current iteration |
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*/ |
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protected $len; |
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/** |
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* @var string[] Prefixes of current length |
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*/ |
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protected $prefixes; |
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/** |
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* @var string[] Strings being merged |
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*/ |
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protected $strings; |
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/** |
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* @var string[] Suffixes of current length |
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*/ |
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protected $suffixes; |
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/** |
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* Get the shortest string that contains all given strings |
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* |
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* @param string[] $strings |
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* @return string |
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*/ |
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public function getShortest(array $strings): string |
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{ |
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$this->strings = array_unique($strings); |
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$this->sortStrings(); |
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$this->removeEmptyStrings(); |
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$this->removeFullyOverlappingStrings(); |
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if (isset($this->strings[1])) |
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{ |
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// Start with the longest partial match possible, which is equal to the length of the |
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// second longest string minus 1 |
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$this->len = strlen($this->strings[1]); |
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while (--$this->len > 0) |
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{ |
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$this->mergeStrings(); |
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} |
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} |
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return implode('', $this->strings); |
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} |
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/** |
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* Compare given strings |
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*/ |
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protected static function compareStrings(string $a, string $b): int |
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{ |
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$aLen = strlen($a); |
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$bLen = strlen($b); |
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if ($aLen !== $bLen) |
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{ |
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// Longest first |
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return $bLen - $aLen; |
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} |
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// Lexical order |
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return ($a > $b) ? 1 : -1; |
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} |
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/** |
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* Match and merge a string by key |
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* |
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* @param integer $leftKey Left string's key |
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* @return bool Whether a match was found and strings merged |
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*/ |
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protected function mergeString(int $leftKey): bool |
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{ |
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// Temporarily blank this string's prefix from the array to avoid matches |
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$prefix = $this->prefixes[$leftKey]; |
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$this->prefixes[$leftKey] = ''; |
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// Search for a prefix that matches this string's suffix before restoring its prefix |
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$rightKey = array_search($this->suffixes[$leftKey], $this->prefixes, true); |
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$this->prefixes[$leftKey] = $prefix; |
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if ($rightKey === false) |
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{ |
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return false; |
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} |
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$this->mergeStringPair($leftKey, $rightKey); |
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return true; |
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} |
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/** |
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* Merge two stored strings together at current affix length |
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*/ |
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protected function mergeStringPair(int $leftKey, int $rightKey): void |
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{ |
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$this->strings[$leftKey] .= substr($this->strings[$rightKey], $this->len); |
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$this->suffixes[$leftKey] = $this->suffixes[$rightKey]; |
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unset($this->prefixes[$rightKey], $this->strings[$rightKey], $this->suffixes[$rightKey]); |
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} |
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/** |
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* Merge all stored strings using current affix length |
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*/ |
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protected function mergeStrings(): void |
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{ |
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$this->storeAffixes(); |
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// Merge strings whose prefix is identical to their suffix |
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$keys = array_keys(array_intersect_assoc($this->prefixes, $this->suffixes)); |
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$this->mergeStringsGroup($keys); |
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// Merge strings that have a suffix that matches a prefix |
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$keys = array_keys(array_intersect($this->suffixes, $this->prefixes)); |
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$this->mergeStringsGroup($keys); |
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$this->resetKeys(); |
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} |
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/** |
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* Match and merge strings from given group |
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* |
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* @param integer[] $keys List of keys |
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* @return void |
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*/ |
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protected function mergeStringsGroup(array $keys): void |
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{ |
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foreach ($keys as $leftKey) |
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{ |
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if (isset($this->strings[$leftKey])) |
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{ |
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while ($this->mergeString($leftKey)) |
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{ |
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// Keep going |
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} |
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} |
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} |
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} |
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/** |
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* Remove empty strings from the list |
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*/ |
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protected function removeEmptyStrings(): void |
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{ |
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if (end($this->strings) === '') |
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{ |
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array_pop($this->strings); |
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} |
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} |
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/** |
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* Remove fully-overlapping strings from the list |
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*/ |
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protected function removeFullyOverlappingStrings(): void |
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{ |
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// Copy the list of strings ordered by ascending length and create a master string by |
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// concatenating them all |
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$strings = array_reverse($this->strings, true); |
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$all = implode('', $strings); |
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$pos = 0; |
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foreach ($strings as $i => $str) |
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{ |
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// Test whether current string potentially appears in any subsequent, bigger strings |
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$pos += strlen($str); |
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if (strpos($all, $str, $pos) === false) |
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{ |
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continue; |
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} |
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// Iterate over strings from the longest to the one before current string |
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$j = -1; |
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while (++$j < $i) |
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{ |
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if (strpos($strings[$j], $str) !== false) |
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{ |
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unset($this->strings[$i]); |
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break; |
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} |
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} |
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} |
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$this->resetKeys(); |
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} |
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/** |
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* Reset the keys in the string list to remove the gaps |
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*/ |
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protected function resetKeys(): void |
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{ |
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end($this->strings); |
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if (key($this->strings) !== count($this->strings) - 1) |
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{ |
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$this->strings = array_values($this->strings); |
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} |
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} |
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/** |
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* Sort the stored strings |
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*/ |
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protected function sortStrings(): void |
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{ |
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usort($this->strings, [__CLASS__, 'compareStrings']); |
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} |
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/** |
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* Capture and stored affixes of current length |
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* |
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* Will only store affixes from strings that are longer than current affix length |
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*/ |
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protected function storeAffixes(): void |
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{ |
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$this->prefixes = []; |
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$this->suffixes = []; |
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foreach ($this->strings as $str) |
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{ |
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if (strlen($str) <= $this->len) |
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{ |
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break; |
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} |
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$this->prefixes[] = substr($str, 0, $this->len); |
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$this->suffixes[] = substr($str, -$this->len); |
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} |
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} |
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} |
