How many ways? hdu 2157

How many ways?? hdu 2157

#include <iostream>
#include <stdio.h>
#include <cstring>
using namespace std;
int tmp[21][21],ans[21][21],b[21][21];
int N;
void mul(int a[][21],int b[][21])
{
    memset(tmp,0,sizeof(tmp));
    for(int i=1; i<=N; i++)
        for(int j=1; j<=N; j++)
            for(int k=1; k<=N; k++)
            {
                tmp[i][j]+=a[i][k]*b[k][j];
                if(tmp[i][j]>=1000) tmp[i][j]%=1000;
            }
    memcpy(a,tmp,sizeof(tmp));
}
void pow(int a[][21],int b[][21],int k)
{
    memset(a,0,sizeof(a));
    for(int i=1; i<=N; i++)
        a[i][i]=1;
    while(k)
    {
        if(k&1) mul(a,b);
        mul(b,b);
        k>>=1;
    }
}
int main()
{
    int m,k,T,s,t;
    int temp[21][21];
    while(scanf("%d%d",&N,&m)==2)
    {
        if(N==0&&m==0) break;
        memset(b,0,sizeof(b));
        memset(temp,0,sizeof(temp));
        while(m--)
        {
            scanf("%d%d",&s,&t);
            b[++s][++t]=1;
            temp[s][t]=1;
        }
        scanf("%d",&T);
        while(T--)
        {
            memset(ans,0,sizeof(ans));
            scanf("%d%d%d",&s,&t,&k);
            memcpy(b,temp,sizeof(temp));
            pow(ans,b,k);
            printf("%d\n",ans[++s][++t]%1000);
        }
    }
    return 0;
}