zoj3631 Watashi's BG DFS

10000000。注意到最多只有30个物品，那么直接DFS，加点剪枝就好了...

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
using namespace std;
typedef long long ll;
bool cmp(int x,int y)
{
    return x>y;
}
int n,m,k;
int a[44];
int vis[33];
ll sum[33];
ll ans;
void dfs(int x,ll w)
{
    if (ans<w) ans=w;
    if (sum[n]-sum[x-1]+w<=ans) return;
    for (int j=x; j<=n; j++)
    if (!vis[j] && w+a[j]<=m)
    {
        vis[j]=true;
        dfs(j+1,w+a[j]);
        vis[j]=false;
    }
}
int main()
{
//    freopen("in.txt","r",stdin);
    while(~scanf("%d%d",&n,&m))
    {
        for (int i=1; i<=n; i++)
        scanf("%d",&a[i]);
        sort(a+1,a+1+n,cmp);
        memset(sum,0,sizeof sum);
        for (int i=1; i<=n; i++)
        sum[i]=sum[i-1]+(ll)a[i];
        memset(vis,false,sizeof vis);
        ans=sum[n];
        if (ans<=m)
        {
            cout<<ans<<endl;
            continue;
        }
        for (int i=n; i>0; i--)
        if (ans>m)
        {
            ans-=a[i];
        }
        else break;

        dfs(1,0);
        cout<<ans<<endl;
    }
    return 0;
}