1.1.print 1 to n then n-1 to 1.cpp

 #include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>

using namespace std;

using namespace __gnu_pbds;

template <class type1>

#define ll long long int

#define endl "\n"

#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>

using ordered_multiset = tree <type1, null_type, less_equal <type1>, rb_tree_tag, tree_order_statistics_node_update>;

 //ordered_multiset <ll> kek;(declaration for multiorder set)

// ordered_set o_set;(declaration)

//kek.order_of_key(i);(strictly less then i for multi order set)

//o_set.order_of_key(5) ;(strictly less then i for multi order set)

#define yes cout << "YES\n"

#define no cout << "NO\n"

void func(ll n,ll i)

{

     if(n==i)

     {

         cout<<n<<" ";

         return;

     }

     cout<<i<<" ";

     ll x=i;

     func(n,++x);

     

     cout<<i<<" ";

}

int main()

{

    ios_base::sync_with_stdio(0);

    cin.tie(0);

    cout.tie(0);

   

      ll n;

      cin>>n;

      func(n,1);

    return 0;

}