BZOJ4800 [Ceoi2015]Ice Hockey World Championship

一眼meet in the middle

枚举前n/2的所有方案和后n/2的所有方案，排序之后双指针即可

#include<iostream>
#include<cstring>
#include<ctime>
#include<cmath>
#include<algorithm>
#include<iomanip>
#include<cstdlib>
#include<cstdio>
#include<map>
#include<bitset>
#include<set>
#include<stack>
#include<vector>
#include<queue>
using namespace std;
#define MAXN 1100010
#define MAXM 1010
#define ll long long
#define eps 1e-8
#define MOD 1000000007
#define INF 1000000000
int n;
ll m;
ll s1[MAXN],s2[MAXN];
ll v1[MAXN],v2[MAXN];
ll v[MAXN];
ll ans;
int main(){
int i;
scanf("%d%lld",&n,&m);
for(i=1;i<=n;i++){
scanf("%lld",&v[i]);
}
int n1=n>>1;
int n2=n-n1;
int N1=1<<n1;
int N2=1<<n2;
for(i=0;i<n1;i++){
v1[1<<i]=v[i+1];
}
for(i=0;i<n2;i++){
v2[1<<i]=v[n1+i+1];
}
for(i=1;i<N1;i++){
s1[i]=s1[i^(i&-i)]+v1[i&-i];
}
for(i=1;i<N2;i++){
s2[i]=s2[i^(i&-i)]+v2[i&-i];
}
sort(s1,s1+N1);
sort(s2,s2+N2);
int wzh=N2-1;
for(i=0;i<N1;i++){
while((~wzh)&&s2[wzh]+s1[i]>m){
wzh--;
}
ans+=wzh+1;
}
printf("%lld\n",ans);
return 0;
}

/*

*/