方案数背包

方案数背包
当凑面值为0时，有且只有一种方案，初始化，f[0]=1
 1 #include<iostream>
 2 #include<cstdio>
 3 #include<queue>
 4 #include<algorithm>
 5 #include<cmath>
 6 #include<ctime>
 7 #include<set>
 8 #include<map>
 9 #include<stack>
10 #include<cstring>
11 #define inf 2147483647
12 #define For(i,a,b) for(register long long i=a;i<=b;i++)
13 #define p(a) putchar(a)
14 #define g() getchar()
15 //by war
16 //2017.20.28
17 using namespace std;
18 long long v,n;
19 long long f[1000010];//80M
20 long long w[3000];
21 
22 void in(long long &x)
23 {
24     long long y=1;
25     char c=g();x=0;
26     while(c<'0'||c>'9')
27     {
28     if(c=='-')
29     y=-1;
30     c=g();
31     }
32     while(c<='9'&&c>='0')x=x*10+c-'0',c=g();
33     x*=y;
34 }
35 void o(long long x)
36 {
37     if(x<0)
38     {
39         p('-');
40         x=-x;
41     }
42     if(x>9)o(x/10);
43     p(x%10+'0');
44 }
45 int main()
46 {
47     in(v),in(n);
48     For(i,1,v)
49     in(w[i]);
50     f[0]=1;
51     For(i,1,v)
52       For(j,w[i],n)
53         f[j]+=f[j-w[i]];
54     o(f[n]);
55      return 0;
56 }