1844B - Permutations Primes - CodeForces Solution

#include<bits/stdc++.h>
#define int long long
using namespace std;
void init_code(){ 
    #ifndef ONLINE_JUDGE 
    freopen("input.txt", "r", stdin); 
    freopen("output.txt", "w", stdout); 
    #endif // ONLINE_JUDGE
} 
int32_t main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    init_code();
    int t;cin>>t; 
    while(t--){ 
        int n;
        cin>>n; 
        if(n==1) cout<<"1"<<endl;
        else if(n==2) cout<<"2 1"<<endl;
        else if(n==3) cout<<"2 1 3"<<endl; 
        else if(n==4) cout<<"2 1 4 3"<<endl;
        else{
            vector<int>v;
            v.push_back(2);
            for(int i=1;i<=n;i++) if(i!=2)v.push_back(i); 
            swap(v[2],v[n-1]); 
            swap(v[1],v[n/2]);
            for(auto &i:v) cout<<i<<" ";
            cout<<endl;
        }
    }
    return 0;
}