HDU 2157 How many ways?? 关系矩阵+快速幂

 1 #include <stdio.h>
 2 #include <iostream>
 3 #include <string.h>
 4 #include <algorithm>
 5 #include <math.h>
 6 #define MAXX 100010
 7 using namespace std;
 8 
 9 struct matrix
10 {
11     int a[20][20];
12     void init(int n)
13     {
14         for(int i = 0; i < n; i++)
15             for(int j = 0; j < n; j++)
16             {
17                 a[i][j] = 0;
18             }
19     }
20 }s, w;
21 
22 
23 matrix mul(matrix x, matrix y, int n)
24 {
25     matrix c;
26     c.init(n);
27     int i , j;
28     for(i = 0; i < n; i++)
29     {
30         for(j = 0; j < n; j++)
31         {
32             for(int k = 0; k < n; k++)
33             {
34                 c.a[i][j]+=x.a[i][k]*y.a[k][j];
35             }
36             c.a[i][j] %= 1000;
37         }
38     }
39     return c;
40 }
41 
42 matrix poww(matrix a, int k, int n)
43 {
44     matrix x;
45     x.init(n);
46     for(int i = 0; i < n; i++)
47         x.a[i][i] = 1;
48     while(k)
49     {
50         if(k & 1)
51             x = mul(x, a, n);
52         a = mul(a, a, n);
53         k >>= 1;
54     }
55     return x;
56 }
57 
58 int main()
59 {
60     int n ,m, T;
61     int x, y;
62     int ss, ee, k;
63     while(~scanf("%d%d", &n, &m) && n+m)
64     {
65         s.init(n);
66         for(int i = 0;  i < m; i++)
67         {
68             scanf("%d%d",&x, &y);
69             s.a[x][y] = 1;
70         }
71 
72         scanf("%d", &T);
73         for(int i = 0; i < T; i++)
74         {
75             scanf("%d%d%d", &ss, &ee, &k);
76             w = poww(s, k, n);
77             printf("%d\n", w.a[ss][ee]);
78         }
79     }
80 
81 }