KMP

kmp

void getnx(string str,int *nx)
{
int len=str.length();int i=0,k=-1;nx[0]=-1;
while(i<len)if(k==-1||str[i]==str[k])nx[++i]=++k;else k=nx[k];
}
int index(string str,string p)
{
int i=0,j=0;int len1=str.length(),len2=p.length();
if(len1==1&&len2==1)if(str[0]==p[0])return 0;else return -1;
int nx[N];getnx(p,nx);
while(i<len1&&j<len2)
if(j==-1||str[i]==p[j])i++,j++;else j=nx[j];
if(j==len2)return i-len2;else return -1;
}
int Count(string str,string p)
{
int ans=0,i=0,j=0;int nx[N];
int len1=str.length(),len2=p.length();
if(len1==1&&len2==1)if(str[0]==p[0])return 1;else return 0;
getnx(p,nx);
for(i=0;i<len1;i++)
{
    while(j>0&&str[i]!=p[j])j=nx[j];
    if(str[i]==p[j])j++;
    if(j==len2)ans++,j=nx[len2];
}
return ans;
}

exkmp

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=50001;
int nxt[maxn],ex[maxn];
void GETNEXT(char *str)
{
int i=0,j,po,len=strlen(str);
nxt[0]=len;
while(str[i]==str[i+1]&&i+1<len)
i++;
nxt[1]=i;
po=1;
for(i=2;i<len;i++)
{
    if(nxt[i-po]+i<nxt[po]+po)
    nxt[i]=nxt[i-po];
    else
    {
        j=nxt[po]+po-i;
        if(j<0)j=0;
        while(i+j<len&&str[j]==str[j+i])
        j++;
        nxt[i]=j;
        po=i;
    }
}
}
void EXKMP(char *s1,char *s2)
{
int i=0,j,po,len=strlen(s1),l2=strlen(s2);
GETNEXT(s2);
while(s1[i]==s2[i]&&i<l2&&i<len)
i++;
ex[0]=i;
po=0;
for(i=1;i<len;i++)
{
    if(nxt[i-po]+i<ex[po]+po)
    ex[i]=nxt[i-po];
    else
    {
        j=ex[po]+po-i;
        if(j<0)j=0;
        while(i+j<len&&j<l2&&s1[j+i]==s2[j])
        j++;
        ex[i]=j;
        po=i;
    }
}
}