HDU 5000 Clone（离散数学+DP）（2014 ACM/ICPC Asia Regional Anshan Online）

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <iostream>
 5 #include <numeric>
 6 #include <functional>
 7 using namespace std;
 8 typedef long long LL;
 9 
10 const int MAXN = 2010;
11 const int MOD = 1e9 + 7;
12 
13 void update_add(int &a, int b) {
14     a += b;
15     if(a >= MOD) a -= MOD;
16 }
17 
18 int a[MAXN][MAXN], sum[MAXN][MAXN];
19 int b[MAXN];
20 int n, s, T;
21 
22 void solve() {
23     memset(a, 0, sizeof(a));
24     s = accumulate(b, b + n, 0);
25 
26     for(int i = 0; i <= b[0]; ++i) a[0][i] = 1;
27     sum[0][0] = a[0][0];
28     for(int j = 1; j <= s; ++j) sum[0][j] = (sum[0][j - 1] + a[0][j]) % MOD;
29 
30     for(int i = 1; i < n; ++i) {
31         for(int j = 0; j <= s; ++j) {
32             //for(int k = j - b[i]; k <= j; ++k) a[i][j] += a[i - 1][k];
33             if(j - b[i] <= 0) a[i][j] = sum[i - 1][j];
34             else a[i][j] = (sum[i - 1][j] - sum[i - 1][j - b[i] - 1] + MOD) % MOD;
35         }
36         sum[i][0] = a[i][0];
37         for(int j = 1; j <= s; ++j) sum[i][j] = (sum[i][j - 1] + a[i][j]) % MOD;
38     }
39 }
40 
41 void print() {
42     for(int j = 0; j <= s; ++j)
43         printf("%4d", j);
44     puts("");
45     for(int i = 0; i < n; ++i) {
46         for(int j = 0; j <= s; ++j)
47             printf("%4d", a[i][j]);
48         puts("");
49     }
50 }
51 
52 int main() {
53     scanf("%d", &T);
54     while(T--) {
55         scanf("%d", &n);
56         for(int i = 0; i < n; ++i) scanf("%d", &b[i]);
57         sort(b, b + n);
58         solve();
59         //print();
60         printf("%d\n", a[n - 1][s / 2]);
61     }
62 }