noj 2033 一页书的书 [ dp + 组合数 ]

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <stack>
 4 #include <vector>
 5 #include <map>
 6 #include <algorithm>
 7 #include <queue>
 8 
 9 #define ll long long
10 int const N = 25;
11 int const M = 205;
12 int const inf = 1000000000;
13 ll const mod = 1000000007;
14 
15 using namespace std;
16 
17 int n,m;
18 int a[N];
19 ll dp[N][N];
20 ll c[N][N];
21 int T;
22 
23 void ini1()
24 {
25     memset(c,0,sizeof(c));
26     int i,j;
27     for(i=0;i<=30;i++){
28         c[i][0]=1;
29     }
30     for(i=1;i<=30;i++){
31         for(j=1;j<=30;j++){
32             c[i][j] = (c[i-1][j-1]+c[i-1][j])%mod;
33         }
34     }
35 /*
36     for(i=1;i<=10;i++){
37         for(j=0;j<=i;j++){
38             printf(" i=%d j=%d c=%I64d\n",i,j,c[i][j]);
39         }
40     }*/
41 }
42 
43 void ini()
44 {
45     scanf("%d%d",&n,&m);
46     memset(dp,0,sizeof(dp));
47     int i;
48     for(i=1;i<=n;i++){
49         scanf("%d",&a[i]);
50     }
51     dp[0][0]=1;
52 }
53 
54 void solve()
55 {
56     int i,j,k;
57     for(j=1;j<=n;j++){
58         for(i=0;i<=m;i++){
59             for(k=0;k<=min(a[j],i);k++){
60                 dp[i][j] = (dp[i][j] + c[i][k] * dp[i-k][j-1]) %mod;
61             }
62         }
63     }
64 }
65 
66 void out()
67 {
68     printf("%I64d\n",dp[m][n]);
69 }
70 
71 int main()
72 {
73     ini1();
74     //freopen("data.in","r",stdin);
75    // freopen("data.out","w",stdout);
76     scanf("%d",&T);
77     for(int cnt=1;cnt<=T;cnt++)
78     //while(T--)
79     //while(scanf("%d%d",&n,&m)!=EOF)
80     {
81         ini();
82         solve();
83         out();
84     }
85 }