【HDOJ】2604 Queuing

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cstdlib>
 4 
 5 #define MATN 4
 6 
 7 typedef struct mat_st {
 8     int m[MATN][MATN];
 9     mat_st() {
10         memset(m, 0, sizeof(m));
11     }
12 } mat_st;
13 
14 int ans[MATN]={1,2,4,6};
15 int mod;
16 
17 mat_st mult_mat(mat_st a, mat_st b) {
18     mat_st ret;
19     int i, j, k;
20 
21     for (i=0; i<MATN; ++i) {
22         for (j=0; j<MATN; ++j) {
23             for (k=0; k<MATN; ++k)
24                 ret.m[i][j] += a.m[i][k]*b.m[k][j];
25             ret.m[i][j] %= mod;
26         }
27     }
28     return ret;
29 }
30 
31 mat_st pow_mat(mat_st a, int n) {
32     mat_st ret;
33     int i;
34 
35     for (i=0; i<MATN; ++i)
36         ret.m[i][i] = 1;
37 
38     while (n) {
39         if (n & 1)
40             ret = mult_mat(ret, a);
41         a = mult_mat(a, a);
42         n >>= 1;
43     }
44     return ret;
45 }
46 
47 int main() {
48     int l;
49     int i;
50     mat_st e, a;
51 
52     e.m[0][0] = e.m[0][1] = e.m[1][2] = e.m[2][0] = e.m[2][3] = e.m[3][0] = 1;
53     for (i=0; i<MATN; ++i)
54         a.m[0][i] = ans[MATN-1-i];
55 
56     while (scanf("%d %d", &l, &mod) != EOF) {
57         if (l <= 3)
58             printf("%d\n", ans[l]%mod);
59         else {
60             mat_st c = pow_mat(e, l-3);
61             mat_st r = mult_mat(a, c);
62             printf("%d\n", r.m[0][0]);
63 #ifndef ONLINE_JUDGE
64             fflush(stdout);
65 #endif
66         }
67     }
68 
69     return 0;
70 }