practice_5.cpp

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int n,i,nj,j,l;
    bool flip;
    vector<int> x;
    cin>>n;
    x.resize(n);
    std::generate(x.begin(),x.end(),
                    [tmp=n]() mutable{return tmp--;});
    for(i=0;i<n;i++){
        for(j=0,nj=0,flip=true;nj<(2*n)-1;nj++,j-=(1-(2*flip)),flip=((j<n-1)&&flip)){
            cout<<x[j];
        }
        std::rotate(x.begin(),x.begin()+1,x.end());
        cout<<endl;
    }
    return 0;
}