usaco-Money Systems(dp背包)

给出几种硬币，数量不限，问你用着几种硬币能组成价值为n的种类是多少。

第一眼看到，求数量，就想到dp，直接找转移方程dp[i] = dp[i] + dp[i - coin[j]];

/*
  ID: xvoid191
  PROG: money
  LANG: C++
*/
#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
long long coin[30],dp[10001];
int n,v;
int main()
{
    freopen("money.in","r",stdin);
    freopen("money.out","w",stdout);
    scanf("%d %d",&v,&n);
    memset(dp,0,sizeof(dp));
    for(int i = 0; i < v; i++){
        scanf("%d",&coin[i]);
    }
    dp[0] = 1;
    for(int i = 0; i < v; i++){
        for(int j = coin[i]; j <= n; j++ ){
            dp[j] += dp[j - coin[i]];
            }
        }
    printf("%lld\n",dp[n]);

}