Cash Machine poj （多重背包）

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#define N 600000
#define INF 0x3f3f3f3f
#define LL long long
using namespace std;
int v[N], num[N], f[N];
int main()
{
    int n, s;
    while(~scanf("%d%d", &s, &n))
    {
        int i, j;
        for(i = 0; i < n; i++)
            scanf("%d%d", &num[i], &v[i]);
        if(s == 0 || n == 0)/*最后面Hint写的*/
        {
            printf("0\n");
            continue;
        }
        memset(f, 0, sizeof(f));
        for(i = 0; i < n; i++)
        {
            if(v[i]*num[i] >= s)/*完全背包*/
            {
                for(j = v[i]; j <= s; j++)
                    f[j] = max(f[j], f[j - v[i]] + v[i]);
            }
            else
            {
                /*0-1背包*/
                int k = 1;
                while(k < num[i])/*采用了二进制的思想*/
                {
                    for(j = s; j >= k * v[i]; j--)
                        f[j] = max(f[j], f[j - k * v[i]] + k * v[i]);
                    num[i] -= k;
                    k <<= 1;
                }
                for(j = s; j >= num[i]*v[i]; j--)
                    f[j] = max(f[j], f[j - num[i] * v[i]] + num[i] * v[i]);
            }
        }
        printf("%d\n", f[s]);
    }
    return 0;
}