HDU 5863 cjj's string game

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0),eps=1e-8;
void File()
{
    freopen("D:\\in.txt","r",stdin);
    freopen("D:\\out.txt","w",stdout);
}
template <class T>
inline void read(T &x)
{
    char c = getchar(); x = 0;while(!isdigit(c)) c = getchar();
    while(isdigit(c)) { x = x * 10 + c - ‘0‘; c = getchar();  }
}

LL n,MOD=1000000007;
int T,m,k;

struct Matrix
{
    long long A[25][25];
    int R, C;
    Matrix operator*(Matrix b);
};

Matrix X, Y, Z;

Matrix cheng(Matrix a,Matrix b)
{
    Matrix c;
    int i, j, k;
    for (i = 1; i <= a.R; i++)
        for (j = 1; j <= b.C; j++){
            c.A[i][j]=0;
            for (k = 1; k <= a.C; k++)
                c.A[i][j] = (c.A[i][j] + (a.A[i][k] * b.A[k][j]) % MOD) % MOD;
        }
    c.R = a.R; c.C = b.C;
    return c;
}

void init()
{
    memset(X.A, 0, sizeof X.A);
    memset(Y.A, 0, sizeof Y.A);
    memset(Z.A, 0, sizeof Z.A);

    Y.R = 2*(m+1); Y.C = 2*(m+1);
    for (int i = 1; i <= 2*(m+1); i++) Y.A[i][i] = 1;

    X.R = 2*(m+1); X.C = 2*(m+1);

    for(int i=1;i<=m;i++) X.A[i][1]=k*(k-1);
    for(int i=1;i<=m-1;i++) X.A[i][i+1]=k;

    for(int i=m+2;i<=2*m+2;i++) X.A[i][m+2]=k*(k-1);
    for(int i=m+2;i<=2*m+1;i++) X.A[i][i+1]=k;
    X.A[m][2*m+2]=k;

    Z.R = 1; Z.C = 2*(m+1);
    Z.A[1][1]=1;
}

void work()
{
    while (n)
    {
        if (n % 2 == 1) Y = cheng(Y,X);
        n = n >> 1;
        X = cheng(X,X);
    }
    Z = cheng(Z,Y);
    LL ans=0; for(int i=m+2;i<=2*(m+1);i++) ans=(ans+Z.A[1][i])%MOD;
    printf("%lld\n",ans);
}

int main()
{
    scanf("%d",&T);
    while(T--)
    {
        scanf("%lld%d%d",&n,&m,&k);
        init();
        work();
    }
    return 0;
}