PHP 哈夫曼的实现

 <?php
 namespace Test;

 use Iterator;
 use ArrayAccess;
 use Exception;

 // 叶子结点或者连接结点的基类
 class HuffmanBase
 {
     protected $weight;       // 权重
     protected $parent;

     public function setParent($parent)
     {
         $this->parent = $parent;
     }

     public function getWeight()
     {
         return $this->weight;
     }

     public function getParent()
     {
         return $this->parent;
     }
 }

 // 叶子结点
 class HuffmanLeafNode extends HuffmanBase
 {
     protected $code;   // 需要编码的字母

     public function __construct($weight,$code,$parent = null)
     {
         if(!is_int($weight) || $weight <= 0 || is_null($code))
         {
             throw new Exception('Param is error!' .__FILE__.__LINE__);
         }
         $this->weight = abs($weight);
         $this->code = $code;
         $this->parent = $parent;
     }

     public function getCode()
     {
         return $this->code;
     }
 }

 // 连接结点
 class HuffmanJoinNode extends HuffmanBase
 {
     protected $lChild;
     protected $rChild;

     public function __construct($weight = 0,$lChild = null,$rChild = null)
     {
         $this->weight = $weight;
         $this->rChild = $rChild;
         $this->lChild = $lChild;
     }

     public function setWeight($leftWeight,$rightWeight)
     {
         if(!is_int($this->rChild) || !is_int($this->lChild))
         {
             throw new \Exception("Please initialize the left child or the right child!\n");
         }
         $this->weight = $leftWeight + $rightWeight;
     }

     public function setChild($child,$leftOrRight)
     {
         if('left' == $leftOrRight)
         {
             $this->lChild = $child;
         }
         elseif('right' == $leftOrRight)
         {
             $this->rChild = $child;
         }
         else
         {
             throw new \Exception("Please input 'left' or 'right' to leftOrRight!\n");
         }
     }

     public function getChild($leftOrRight)
     {
         if('left' == $leftOrRight)
         {
             return $this->lChild;
         }
         elseif('right' == $leftOrRight)
         {
             return $this->rChild;
         }
         else
         {
             throw new \Exception("Please input 'left' or 'right' to leftOrRight!\n");
         }
     }
 }

 // 哈夫曼树
 class HuffmanTree implements \ArrayAccess,\Iterator
 {
     protected $nodes = array();

     public function &getAllNodes()
     {
         return $this->nodes;
     }

     public function offsetExists($offset)
     {
         // TODO: Implement offsetExists() method.
         return isset($this->nodes[$offset]);
     }

     public function offsetGet($offset)
     {
         // TODO: Implement offsetGet() method.
         if(isset($this->nodes[$offset]))
         {
             return $this->nodes[$offset];
         }
         else
         {
             return null;
         }
     }

     public function offsetSet($offset,$value)
     {
         // TODO: Implement offsetSet() method.
         if(!($value instanceof HuffmanBase))
         {
             throw new Exception('Param is error!' .__FILE__.__LINE__);
         }

         if(is_null($offset))
         {
             $this->nodes[] = $value;
         }
         else
         {
             $this->nodes[$offset] = $value;
         }
     }

     public function offsetUnset($offset)
     {
         // TODO: Implement offsetUnset() method.
         unset($this->nodes[$offset]);
     }

     public function current()
     {
         // TODO: Implement current() method.
         return current($this->nodes);
     }

     public function key()
     {
         // TODO: Implement key() method.
         return key($this->nodes);
     }

     public function next()
     {
         // TODO: Implement next() method.
         next($this->nodes);
     }

     public function rewind()
     {
         // TODO: Implement rewind() method.
         reset($this->nodes);
     }

     public function valid()
     {
         // TODO: Implement valid() method.
         return $this->offsetExists(key($this->nodes));
     }

     public function length()
     {
         return count($this->nodes);
     }
 }

 // 从[$left,$right]区间选择parent=0并且weight最小的两个结点，其序号分别为$minNode1,$minNode2;
 function selectTwoMinWeightNode(HuffmanTree &$huffmanTree,$left,$right,&$minNode1,&$minNode2)
 {
     $left = abs($left);
     $right = abs($right);

     if(!is_int($left) || !is_int($right) || $left == $right)
     {
         throw new Exception('Param is error!' .__FILE__.__LINE__);
     }

     if($left > $right)
     {
         $tmp = $left;
         $left = $right;
         $right = $tmp;
     }

     $nodes = $huffmanTree->getAllNodes();
     if(!isset($nodes[$right]))
     {
         throw new Exception('Over the array index!'.__FILE__.__LINE__);
     }

     $tmp = array();
     for($i = $left;$i <= $right; ++$i)
     {
         $huffmanNode = $huffmanTree[$i];
         if(!is_null($huffmanNode->getParent()))
         {
             continue;
         }
         $tmp[$i] = $huffmanNode->getWeight();
     }

     if(count($tmp) <= 1)
     {
         throw new Exception('Not enough number!'.__FILE__.__LINE__);
     }
     asort($tmp,SORT_NUMERIC);
     $t = array_keys($tmp);
     $minNode1 = $t[0];
     $minNode2 = $t[1];
 }

 // (编码 => 权重)
 $nodes = array('A' => 3, 'B' => 4, 'C' => 7, 'D' => 10);

 $huffmanTree = new HuffmanTree();

 // 初始化哈夫曼树的叶子结点
 foreach($nodes as $code => $weight)
 {
     $huffmanNode = new HuffmanLeafNode($weight,$code);
     $huffmanTree[] = $huffmanNode;
 }

 $leafCount = $huffmanTree->length();        // 叶子结点的数量（大于1的值）
 $nodeCount = 2 * $leafCount -1 ;           // 哈夫曼树结点的数量

 // 初始化哈夫曼树的非叶子结点(如果编译器未优化，--$i应该是比$i++效率高点的)
 for($i = $nodeCount - $leafCount;$i >= 1; --$i)
 {
     $huffmanNode = new HuffmanJoinNode();
     $huffmanTree[] = $huffmanNode;
 }

 // 建立哈夫曼树
 for($i = $leafCount;$i < $nodeCount; ++$i)
 {
     selectTwoMinWeightNode($huffmanTree,0,$i-1,$minNode1,$minNode2);
     $huffmanNode1 = $huffmanTree[$minNode1];
     $huffmanNode2 = $huffmanTree[$minNode2];
     $huffmanNode1->setParent($i);
     $huffmanNode2->setParent($i);
     $huffmanTree[$i]->setChild($minNode1,'left');
     $huffmanTree[$i]->setChild($minNode2,'right');
     $huffmanTree[$i]->setWeight($huffmanNode1->getWeight(),$huffmanNode2->getWeight());
 }

 // 从叶子到根的遍历，得到字母的编码
 $huffmanCode = array();
 for($i = 0;$i < $leafCount; ++$i)
 {
     $leafNode = $huffmanTree[$i];
     $code = $leafNode->getCode();
     $reverseCode = array();
     for($c = $i,$pi = $leafNode->getParent();!is_null($pi);$pi = $huffmanTree[$pi]->getParent())
     {
         $huffmanNode = $huffmanTree[$pi];
         if($huffmanNode->getChild('left') === $c)
         {
             $reverseCode[] = 0;
         }
         elseif($huffmanNode->getChild('right') === $c)
         {
             $reverseCode[] = 1;
         }
         else
         {
             throw new Exception('Something error happened!' .__FILE__.__LINE__);
         }
         $c = $pi;
     }
     $huffmanCode[$code] = array_reverse($reverseCode);
 }

 foreach($huffmanCode as $key => $value)
 {
     $s = implode(',',$value);
     echo $key. " : " .$s ."\n";
 }

运行结果：

运行环境：

ArrayAccess  ：(PHP 5 >= 5.0.0, PHP 7)