[HDU2157]How many ways??（矩阵乘法）

题目描述

题解

代码

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
const int Mod=1000;
int n,m,x,y,T,k;
struct hp{int a[50][50];}A,unit,ans;

inline hp cheng(hp a,hp b)
{
hp ans;
memset(ans.a,0,sizeof(ans.a));
for (int i=1;i<=n;++i)
for (int j=1;j<=n;++j)
for (int k=1;k<=n;++k)
ans.a[i][j]=(ans.a[i][j]+a.a[i][k]*b.a[k][j]%Mod)%Mod;
return ans;
}
inline hp matrix_fast_pow(hp a,int p)
{
hp ans=unit;
for (;p;p>>=1,a=cheng(a,a))
if (p&1)
ans=cheng(ans,a);
return ans;
}
int main()
{
while (~scanf("%d%d",&n,&m))
{
if (!n&&!m) return 0;
memset(unit.a,0,sizeof(unit.a));
for (int i=1;i<=n;++i) unit.a[i][i]=1;
memset(A.a,0,sizeof(A.a));
for (int i=1;i<=m;++i)
{
scanf("%d%d",&x,&y);
x++; y++;
A.a[x][y]=1;
}
scanf("%d",&T);
for (int i=1;i<=T;++i)
{
scanf("%d%d%d",&x,&y,&k);
x++; y++;
ans=matrix_fast_pow(A,k);
printf("%d\n",ans.a[x][y]);
}
}
}