KMP

#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;

void GetNext(char *str,int next[])
{
    int j,k;
    j=0;k=-1;next[0]=-1;
    while(str[j]!='\0')
    {
        if(k==-1 || str[j]==str[k])
        {
            j++;k++;
            next[j]=k;
        }
        else k=next[k];
    }
}

int KMPIndex(char *s,char *t)
{
    int lent=strlen(t);
    int next[100],i=0,j=0,v;
    GetNext(t,next);
    while(s[i]!='\0' && t[j]!='\0')
    {
        if(j==-1 || s[i]==t[j])
        {
            i++;j++;
        }
        else j=next[j];
    }
    if(j>=lent) v=i-lent;
    else v=-1;
    return v;
}

int main()
{
    char s[]="ababcabsds";
    char t[]="abcd";
    cout<<KMPIndex(s,t);
    return 0;
}