PHP implements KMP algorithm

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Release： 2023-03-23 14:26:01

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function cal_next($str){
    $next[0] = -1;//next[0]初始化为-1

    $i=0;    $j = -1;    $len=strlen($str);    while($i<$len){ 
           if($j===-1 || $str[$i]===$str[$j]){            $i++;            $j++;            $next[$i]=$j;
        }else{            $j=$next[$j];
        }
    }    return $next;
}$str=&#39;ABCDABD&#39;;$next=cal_next($str);
var_dump($next);function search($str,$search){
    $next=cal_next($search);    $i=0;    $j=0;    $lenStr=strlen($str);    $lenSearch=strlen($search);    while($i<$lenStr && $j<$lenSearch){
            if($j===-1 || $str[$i]===$search[$j]){
            //$i 主串的不后退，移动模式串。为什么没有$j===0，因为如果有$j++为1，下一步是判断$str[$i]===$search[1]，跳过了$search[0]
            $i++;            $j++;
        }else{            $j=$next[$j];
        }
    }    if($j===$lenSearch){        return $i-$j;
    }    return -1;
}


var_dump(search($str,&#39;ABD&#39;));

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Reference

[KMP算法（1）：如何理解KMP](https://segmentfault.com/a/1190000008575379)

[字符串匹配的KMP算法](http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html)

 [KMP算法最浅显理解](https://blog.csdn.net/starstar1992/article/details/54913261)

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function cal_next($str){
    $next[0] = -1;//next[0]初始化为-1

    $i=0;    $j = -1;    $len=strlen($str);    while($i<$len){        if($j===-1 || $str[$i]===$str[$j]){            $i++;            $j++;            $next[$i]=$j;
        }else{            $j=$next[$j];
        }
    }    return $next;
}$str=&#39;ABCDABD&#39;;$next=cal_next($str);
var_dump($next);function search($str,$search){
    $next=cal_next($search);    $i=0;    $j=0;    $lenStr=strlen($str);    $lenSearch=strlen($search);    while($i<$lenStr && $j<$lenSearch){        if($j===-1 || $str[$i]===$search[$j]){//$i 主串的不后退，移动模式串。为什么没有$j===0，因为如果有$j++为1，下一步是判断$str[$i]===$search[1]，跳过了$search[0]
            $i++;            $j++;
        }else{            $j=$next[$j];
        }
    }    if($j===$lenSearch){        return $i-$j;
    }    return -1;
}


var_dump(search($str,&#39;ABD&#39;));

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Reference

[KMP算法（1）：如何理解KMP](https://segmentfault.com/a/1190000008575379)

[字符串匹配的KMP算法](http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html)

 [KMP算法最浅显理解](https://blog.csdn.net/starstar1992/article/details/54913261)

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