php 兌現KMP演算法

php 實現KMP演算法
/**
* KMP演算法的PHP實現
*
* @author zhaojiangwei 2011/10/22 10:28
*/

class KMP{
private $next = NULL; //模式串T的next數組
private $t = NULL; //模式串
private $str = NULL; //主串

public function KMP($str){
$this->str = str_split($str);
$this->next = array();
}

//返回主串的長度
public function getStrCount(){
return count($this->str);
}

//返回結果
public function getStrPos($substr){
$substr = str_split($substr);
$this->getNext($substr);
$strCount = $this->getStrCount();
$substrCount = count($substr);
$subIndex = 0;//子串的起始比較位置
$strIndex = 0;//主串目前的比較到的位置

while($subIndex < $substrCount && ($strCount - $strIndex) >= ($substrCount - $subIndex)){
if($subIndex == -1 || $this->str[$strIndex] == $substr[$subIndex]){
$subIndex ++;
$strIndex ++;
}else{
$subIndex = $this->next[$subIndex];
}
}

if($subIndex == $substrCount){
return $strIndex - $substrCount;
}else{
return false;
}
}

//求模式串的NEXT數組
public function getNext($t){
if(!is_array($t)){
$t = str_split($t);
}

$this->next[0] = -1;
$count = count($t);

$i = 0;
$j = -1;
while($i < $count){
if($j == -1 || $t[$i] == $t[j]){
$j ++;
$i ++;

if($t[$i] == $t[$j]){
$this->next[$i] = $this->next[$j];
}else{
$this->next[$i] = $j;
}
}else{
$j = $this->next[$j];
}
}

return $this->next;
}

}

