一道ACM题，字符串前缀，找不出递推的规律。解决办法

#include<iostream>
#include<cstring>
using namespace std;
const int MM=1000000007;
int dp[200005],next[200005];
char t[200005];
void GetNext(int len){
     next[0]=-1;
     int i=0,j=next[i];
     while(i<len){
         if(j==-1 || t[i]==t[j]){
             i++;
             j++;
             next[i]=j;
         }
         else
             j=next[j];
     }
}
int main(){
    int tt,len,sum;
    scanf("%d",&tt);
    while(tt--){
        scanf("%s",t);
        len=strlen(t);
        GetNext(len);
        memset(dp,0,sizeof(dp));
        sum=0;
        for(int i=1;i<=len;i++){
            dp[i]=(dp[next[i]]+1)%MM;
            sum=(sum+dp[i])%MM;
        }
        printf("%d\n",sum);
    }
return 0;
}