[cpp]
#include "stdafx.h"
#include <iostream>
using namespace std;
void get_next(char*t, int next[ ]){
int t_len=strlen(t);
int i=0; //求解每个next[i]
next[0]=-1; //递推基本条件,然后求解next[i+1]
int j=-1; //向后递推位置下标
/*
next[i]=k =>T0...Tk-1=Ti-k...Ti-1
求解next[i+1]
1> 如果T0..Tk-1Tk=Ti-k...Ti-1Ti=>next[i+1]=k+1=next[i]+1;
2>Tk<>Ti,next[k]=k', 如果Ti=Tk'=>next[i+1]=k'+1=next[k]+1=next[next[i]]+1;
3>依次递推 最后情况next[i+1]=next[0]+1=0,即
*/
while(i<t_len)
{
if(j==-1 ||t[i]==t[j]) //j==-1证明已经与t[0]不匹配了，此时next[i+1]=0
{
i++;
j++;
next[i]=j;
}
else
{
j=next[j];
}
}
}
int KMP(char *s,char *t){
int s_len=strlen(s);
int t_len=strlen(t);
int i=0;
int j=0;
int *next=new int[t_len];
get_next(t,next);
if(t_len>s_len) return -1;
while(i<s_len&&j<t_len){
if(j==-1||s[i]==t[j]){
i++;
j++;
}
else{
j=next[j];
}
}//end while
if(j>=t_len)
return i-j;
else
return -1;
}
int main(void)
{
char *s="abcdasdefghijklmnefgh";
char *t="efgh";
cout<<KMP(s,t)<<endl;
return 0;
}