洛谷P1466 集合 Subset Sums_01背包水题

不多解释，适当刷刷水…
Code:

#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn = 10000000 + 3;
long long f[maxn];
int main()
{
    int n, sumv = 0;
    scanf("%d",&n);
    for(int i = 1;i <= n; ++i) sumv += i;
    if(sumv % 2 != 0) {printf("0"); return 0;}
    sumv >>= 1;
    f[0] = 1;
    for(int i = 1;i <= n; ++i)
        for(int v = sumv;v >= i; --v)
        {
            f[v] += f[v - i];
        }
    printf("%lld",f[sumv] / 2);
    return 0;
}