HDU1867.cpp KMP中發生不匹配時，j=next[j],j的含義

#include<stdio.h>
#include<string.h>
#define size 100009
void getnext(char *p,int *next)
{
        int i,j;
        next[0]=-1;
        i=0,j=-1;
        int len=strlen(p);
        while(i<len)
        {
                if(j==-1 || p[i]==p[j])i++,j++,next[i]=j;
                else j=next[j];
        }
}

void kmp(char *s,char *p,int *next,char *ans)
{
        int i,j;
        i=0,j=0;
        int l1=strlen(s);
        int l2=strlen(p);
        if(l1>l2)
            i=l1-l2;
        while(i<l1 && j<l2)
        {
                if(j==-1 || s[i]==p[j])i++,j++;
                else j=next[j];
        }
        strcpy(ans,s);
        strcpy(ans+l1,p+j);

}
int main()
{
        char s[size],t[size],ans1[size*2],ans2[size*2];
        int next1[size],next2[size];
        while(~scanf("%s%s",s,t))
        {
                getnext(s,next1);
                getnext(t,next2);
                kmp(s,t,next2,ans1);
                kmp(t,s,next1,ans2);
                int l1=strlen(ans1);
                int l2=strlen(ans2);
                if(l1>l2)
                    printf("%s\n",ans2);
                else if(l1<l2)
                    printf("%s\n",ans1);
                else if(l1==l2)
                {
                        if(strcmp(ans1,ans2)>0)
                            printf("%s\n",ans2);
                        else printf("%s\n",ans1);
                }

        }
        return 0;
}