Tries, Conversions and Field GoalsA RUGBY (LEAGUE) FAN’S GUIDE TO TRIE DATA STRUCTURES

Who am I?Mark Baker

Design and Development ManagerInnovEd (Innovative Solutions for Education) Ltd

Coordinator and Developer of:Open Source PHPOffice library

PHPExcel, PHPWord,PHPPowerPoint, PHPProject, PHPVisioMinor contributor to PHP core

@Mark_Baker

https://github.com/MarkBaker

http://uk.linkedin.com/pub/mark-baker/b/572/171

Tries – What is a Trie? A trie is a key/value data structure that stores the information about the key of each node in the path from the root to the node, rather than in the node itself.

Each path between the root and a leaf represents a key.

Each transition between two nodes is labelled with a single character from a key.

Typically (though not always) the keys will be string values.

Tries – What is a Trie? A special marker on each node indicates whether or not it represents the end of a key.

An “end” node may still have child nodes.

Tries – What is a Trie? Methods:

◦ Insert(key, value)◦ Delete(key)◦ Search(key)

Tries – What is a Trie? Used for:

◦ Dictionary lookups◦ Predictive text / Autocomplete◦ Spell checkers◦ DNA sequencing◦ Burst Sort

Conversions – Tries in PHPclass TrieNode {     /**      * Array of child nodes indexed by next character      *      * @var   TrieNode[]      **/     public $children = array();

    /**      * Flag indicating if this node is an end node      *      * @var   boolean      **/     public $valueNode = false;

    /**      * Data value (empty unless this is an end node)      *      * @var   mixed      **/     public $value; }

Conversions – Tries in PHP

Conversions – Tries in PHP

Conversions – Tries in PHP class Trie {

    /**      * Adds a new entry to the Trie      * If the specified node already exists, then its value will be overwritten      *      * @param   mixed   $key     Key for this node entry      * @param   mixed   $value   Data Value for this node entry      * @return  null      */     public function add($key, $value = null) {         $trieNodeEntry = $this->getTrieNodeByKey($key, true);         $trieNodeEntry->valueNode = true;         $trieNodeEntry->value = $value;     }

}

Conversions – Tries in PHP

Conversions – Tries in PHP class Trie {

    /**      * Backtrack toward the root of the Trie, deleting as we go, 

* until we reach a node that we shouldn't delete      *      * @param   TrieNode   $trieNode   This node entry      * @param   mixed       $key        The full key for this node entry      * @return  null      */     private function delete_backtrace(TrieNode $trieNode, $key) {         $previousKey = substr($key, 0, -1);         $thisChar = substr($key, -1);         $previousTrieNode = $this->getTrieNodeByKey($previousKey);         unset($previousTrieNode->children[$thisChar]);

        if ((count($previousTrieNode->children) == 0) && (!$previousTrieNode->valueNode)) {             $this->delete_backtrace($previousTrieNode, $previousKey);         }     }

    /**      * Delete a node in the Trie      *      * @param   mixed   $key   The key for the node that we want to delete      * @return  boolean        Success or failure, false if the node didn't exist      */     public function delete($key) {         $trieNode = $this->getTrieNodeByKey($key);         if (!$trieNode) {             return false;         }

        if (!empty($trieNode->children)) {             $trieNode->valueNode = false;             $trieNode->value = null;         } else {             $this->delete_backtrace($trieNode, $key);         }

        return true;     }

}

Conversions – Tries in PHP function buildTries($fileName) {     $playerData = json_decode(         file_get_contents($fileName)     );

    $trie = new \Trie();     foreach($playerData as $player) {         $playerName = $player->surname . ', ' . $player->firstname;         $trie->add($playerName, $player);     }     return $trie; }

/* Populate the trie  */ $tries = buildTries(__DIR__ . '/RugbyData.json');

/* Do some searches */ $searchResult = $tries->search($searchName); if (empty($searchResult)) {     echo 'No matches found', PHP_EOL; } else {     $players = array_slice($searchResult, 0, $limit);     foreach($players as $player) {         echo $player->surname, ', ', $player->firstname, PHP_EOL;     } }

Conversions – Tries in PHP/usr/mark/presentations/tries php trieSearch.php HallLoad Time: 0.0221 sCurrent Memory: 4499.16 kPeak Memory: 4569.01 k

Hall, BillHall, HarryHall, JamesHall, MartinHalliwell, BillyHalliwell, CHalliwell, FrankHalliwell, Jimmy

Search Time: 0.0045 sCurrent Memory: 4500.70 kPeak Memory: 4569.01 k

Field Goals – Compressed Tries

Field Goals – Patricia TriesPatricia - Practical Algorithm to Retrieve Information Coded in Alphanumeric

Field Goals

Questions?