4800: [Ceoi2015]Ice Hockey World Championship

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int n;
ll a[1<<21],b[1<<21],w[50],m,ans;
int ta,tb;

void dfs(int x,int lim,ll now,ll *v,int &cnt)
{
if(now>m) return;
if(x>lim){v[++cnt]=now;return ;}
dfs(x+1,lim,now,v,cnt),dfs(x+1,lim,now+w[x],v,cnt);
}

void work()
{
sort(a+1,a+ta+1);sort(b+1,b+tb+1);
for(int i=1,j=tb;i<=ta&&j>=1;i++)
{
while(a[i]+b[j]>m&&j>=1) j--;
ans+=j;
}
printf("%lld\n",ans);
}

void init()
{
scanf("%d%lld",&n,&m);
for(int i=1;i<=n;i++) scanf("%lld",&w[i]);
dfs(1,n>>1,0,a,ta);
dfs((n>>1)+1,n,0,b,tb);
}

int main()
{
init();
work();
return 0;
}