Search optimization pruning - cattle off more school second field F

I tried many critical search and pruning, and finally found still like the pressure of better quality

#include <bits/stdc++.h>
using namespace std;
// #define IO
#define fi first
#define se second
#define pb push_back
#define mk make_pair
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid+1,r
#define rep(i,s,t) for(int i=s;i<t;i++)
#define REP(i,s,t) for(int i=s;i<=t;i++)
#define DOW(i,s,t) for(int i=s;i>=t;i--)
#define dow(i,s,t) for(int i=s;i>t;i--)
#define clr(a,b) memset(a,b,sizeof(a))
#define debug(x) cout<<#x<<' '<<x<<endl
 
typedef long long ll;
typedef pair<int,int>pii;
inline int lowbit(int x){ return x&(-x); }
template<typename T>
inline void read(T&x){
    x=0;int f=1;char ch=getchar();
    while(ch<'0' ||ch>'9'){ if(ch=='-')f=-1; ch=getchar(); }
    while(ch>='0' && ch<='9'){ x=x*10+ch-'0'; ch=getchar(); }
    x*=f;
}
const int N = 110;
ll g[N][N];
ll n,ans;
 
void dfs(int mask,int num,int pre,ll preans){
    if(num<<1==n){
        ans=max(ans,preans);return;
    }
    IF (N- . 1 -pre NUM + <n-/ 2 ) return ;        // represents all subsequent even number are selected, nor meet the conditions (set can not be selected from n / 2 elements), direct return ( optimal pruning) 
    for ( int I = pre + . 1 ; I <n-; I ++ ) { 
        LL nowans = preans; 
        REP (J, 0 , n-) {
             IF (& mask ( . 1 << J)) nowans- = G [ I] [J];
             the else nowans + = G [I] [J]; 
        } 
        DFS (mask | ( . 1 << I), NUM + . 1 , I, nowans); 
    } 
} 
int main () {
    CIN >> n-; = n-<< . 1 ; 
    REP (I, 0 , n-) REP (J, 0 , n-) Read (G [I] [J]); 
    LL nowans = 0 ;         // will now first into another set point 
    REP (I, 0 , n-) nowans + = G [ 0 ] [I]; 
    DFS (( . 1 << 0 ), . 1 , 0 , nowans); 
    the printf ( " % LLD \ n- " , ANS);
     return  0 ; 
}

And then there's a different idea of ​​the search, beginning two sets are empty, and then to fill in two sets of elements, it will be a lot less redundant search

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll n,vis[30],mp[30][30],ans;


int s1[30],s2[30],top1,top2;
void dfs(int pos,ll now){
    if(pos>2*n){
        ans=max(ans,now);
        return;
    }
    if(top1<n){
        s1[++top1]=pos;
        ll nxt=now;
        for(int i=1;i<=top2;i++)
            nxt+=mp[pos][s2[i]];
        dfs(pos+1,nxt);
        top1--;
    }
    if(top2<n){
        s2[++top2]=pos;
        ll nxt=now;
        for(int i=1;i<=top1;i++)
            nxt+=mp[pos][s1[i]];
        dfs(pos+1,nxt);
        top2--;
    }
}

int main(){
    cin>>n;
    for(int i=1;i<=2*n;i++) 
        for(int j=1;j<=2*n;j++)
            scanf("%d",&mp[i][j]);
    ans=0;
    dfs(1,0);
    cout<<ans<<endl;
}
/*
(28,14)=
*/