2019牛客暑期多校训练营（第二场）F

C(2*n,n)是4e7，总状态是4e7种，然后转移,o(n)直接从相邻的状态转移。和裸暴力没啥区别.

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

#define VNAME(value) (#value)
#define bug printf("*********\n");
#define debug(x) cout<<"["<<VNAME(x)<<" = "<<(x)<<"]"<<endl;
#define mid (l+r)/2
#define chl 2*k+1
#define chr 2*k+2
#define lson l,mid,chl
#define rson mid+1,r,chr
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a));

const long long mod=1e9+7;
const int maxn=1e6+5;
const int INF=0x7fffffff;
const LL inf=0x3f3f3f3f;
const double eps=1e-8;
void f() {
#ifndef ONLINE_JUDGE
    freopen("dat.in", "r", stdin);
#endif // ONLINE_JUDGE
}
#ifndef ONLINE_JUDGE
clock_t start=clock();
#endif // ONLINE_JUDGE
int n,m;
int mp[30][30];
LL sum,ans;
int ar[15],br[15]; //a b 个表示一个集合
int la,lb;
void dfs(int num) {   //选n位
    if(la>n||lb>n)return ;  
    if(la==n&&lb==n) {  //如果各选了 n 位就更新答案
        ans=max(sum,ans);
        return ;
    } else {
        if(la<n) { 
            LL tmp=0;
            for(int i=0; i<lb; i++) {   //选到 a 集合
                tmp+=mp[num][br[i]];
            }
            sum+=tmp;
            ar[la++]=num;
            dfs(num+1);
            ar[--la];
            sum-=tmp;
        }
        if(lb<n) {
            LL tmp=0;
            for(int i=0; i<la; i++) {       //选到 b 集合
                tmp+=mp[num][ar[i]];
            }
            sum+=tmp;
            br[lb++]=num;
            dfs(num+1);
            br[lb--];
            sum-=tmp;
        }
    }
}

int main() {
    f();
    scanf("%d", &n);
    m = 2 * n;
    for(int i = 0; i < m; ++i) {
        for(int j = 0; j < m; ++j) {
            scanf("%d", &mp[i][j]);
        }
    }
    dfs(0);
    printf("%lld\n",ans);

#ifndef ONLINE_JUDGE
    debug((1.0*(clock()-start)/1000));
#endif // ONLINE_JUDGE

    return 0;
}