【bzoj4800】: [Ceoi2015]Ice Hockey World Championship dfs

 1 #include <cstdlib>
 2 #include <cstring>
 3 #include <cmath>
 4 #include <cstdio>
 5 #include <algorithm>
 6 using namespace std;
 7 #define ll long long
 8 
 9 
10 ll n,m,mid,ans;
11 ll c[50],a[2][1100000],ca[2];
12 
13 void dfs(int p,int x,ll cost){
14     if (cost>m) return;
15     if ((x>=mid && p==0) || (x>=n && p==1)){
16         a[p][++ca[p]]=cost;
17         return;
18     }
19     dfs(p,x+1,cost+c[x+1]);
20     dfs(p,x+1,cost);
21 }
22 
23 int main(){
24     scanf("%lld%lld",&n,&m);
25     for (int i=1;i<=n;i++) scanf("%lld",&c[i]);
26     mid=n/2;
27     dfs(0,0,0);
28     dfs(1,mid,0);
29     sort(a[0]+1,a[0]+ca[0]+1);
30     sort(a[1]+1,a[1]+ca[1]+1);
31     for (int l=1,r=ca[1];l<=ca[0] && r>=1;ans+=r,l++) while (a[0][l]+a[1][r]>m) r--;
32     printf("%lld\n",ans);
33     return 0;
34 }