USACO stamps

　　这道题的意思是给你K中邮票， 每种邮票有无数个， 你可以从中选取一些邮票， 但是所选取的邮票总数不能超过N个， 问用K种邮票能组成连续几个面值？完全背包的变体， 直接定义f[i][j]为前i种邮票组成j最少需要多少张，剩下的就看代码：

/*
ID: m1500293
LANG: C++
PROG: stamps
*/

#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;
int stamps[55];
short f[2][2000000+2];

int main()
{
freopen("stamps.in", "r", stdin);
freopen("stamps.out", "w", stdout);
int K, N;
scanf("%d%d", &K, &N);
int maxstamps = 0;
for(int i=1; i<=N; i++)
{
scanf("%d", &stamps[i]);
maxstamps = max(maxstamps, stamps[i]);
}
memset(f, 0x3f, sizeof(f));
f[0][0] = 0;
for(int i=1; i<=N; i++)
{
memset(f[i%2], 0x3f, sizeof(f[0]));
for(int j=0; j<=maxstamps*K; j++)
{
if(j >= stamps[i])
f[i%2][j] = min(f[(i-1)%2][j], (short)(f[i%2][j-stamps[i]]+1));
else
f[i%2][j] = f[(i-1)%2][j];
}
}
int res = 0;
for(int j=1; j<=maxstamps*K; j++)
{
if(f[N%2][j] <= K) res = j;
else  break;
}
printf("%d\n", res);
return 0;
}