How many ways?? - hdu2157（矩阵快速幂-模板）

分析：求Map^k，刚开始没有用快速幂，TLE了

 

代码如下：

====================================================================================================

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<queue>
using namespace std;

const int MAXN = 30;
const int mod  = 1000;

struct Matrix
{///定义一个矩阵
    int edge[MAXN][MAXN];
};

int N;

void Mul(Matrix a, Matrix b, Matrix &ans)
{///a * b -> ans
    memset(ans.edge, 0, sizeof(ans.edge));

    for(int i=0; i<N; i++)
    for(int j=0; j<N; j++)
    for(int p=0; p<N; p++)
    {
        ans.edge[i][j] += a.edge[i][p] * b.edge[p][j];
        ans.edge[i][j] %= mod;
    }
}
void QuickPow(Matrix Map, int k, Matrix &ans)
{///Map^k -> ans
    memset(ans.edge, 0, sizeof(ans.edge));

    for(int i=0; i<N; i++)
        ans.edge[i][i] = true;

    while(k)
    {
        if(k & 1)
            Mul(ans, Map, ans);
        Mul(Map, Map, Map);

        k /= 2;
    }
}

int main()
{
    int M;

    while(scanf("%d%d", &N, &M), M+N)
    {
        int u, v, k;
        Matrix Map, ans;

        memset(Map.edge, 0, sizeof(Map.edge));

        while(M--)
        {
            scanf("%d%d", &u, &v);
            Map.edge[u][v] = true;
        }

        scanf("%d", &M);

        while(M--)
        {
            scanf("%d%d%d", &u, &v, &k);

            QuickPow(Map, k, ans);

            printf("%d\n", ans.edge[u][v]);
        }
    }

    return 0;
}