HDU 3336 Count the string

//this problem is same like to (POJ)Seek the Name, Seek the Fame
#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#define N 200010
using namespace std;

char a[N];
int Next[N];
int Len;
int dp[N];//dp[i] represents from 1 ~ i strings, how many prefixs are end by i
const int mod = 10007;

void GetNext()
{
    int i = 0, j = Next[0] = -1;
    while (i < Len)
    {
        if (j == -1 || a[i] == a[j])
            Next[++i] = ++j;
        else
            j = Next[j];
    }
}

int main(void)
{
    ios::sync_with_stdio(false);
    int cas;
    cin >> cas;
    while (cas--)
    {
        cin >> Len >> a;
        GetNext();
        int res = 0;
        memset(dp, 0, sizeof(dp));
        for (int i = 1; i <= Len; ++i)
        {
            dp[i] = (dp[Next[i]] + 1) % mod;// eg:(1 + 1) % mod <=> 1 % mod + 1 % mod
            res = (res + dp[i]) % mod;
        }
        cout << res << endl;
    }

    return 0;
}