C - Numbers on Whiteboard.cpp

#include<bits/stdc++.h>
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
 
#define fastio ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
#define printclock cerr<<"Time : "<<1000*(ld)clock()/(ld)CLOCKS_PER_SEC<<"ms\n"
#define MAX 1000000
#define mod 1000000007
#define ll long long int
#define ld long double
#define ull unsigned long long
#define li long int
#define str string
#define fr(i,n) for(ll i = 0; i<n; i++)
#define frj(j,i,n) for(ll j = i; j<n; j++)
#define frev(i,n) for(ll i = n-1; i>=0; i--)
#define all(x) x.begin(),x.end()
#define debug(x) cout << #x << " " << x << endl;
#define println(x) cout << x << "\n";
#define print(x) cout << x << " ";
#define printCase(x) cout << "Case #" << x << ": ";
#define umax(a, b) a=max(a,b);
 
template<class A> void read(vector<A>& v);
template<class T> void read(T& x) {
    cin >> x;
}
void read(double& d) {
    string t;
    read(t);
    d=stod(t);
}
void read(long double& d) {
    string t;
    read(t);
    d=stold(t);
}
template<class H, class... T> void read(H& h, T&... t) {
    read(h);
    read(t...);
}
 
template<class A> void write(A x) {
    cout << to_string(x);
}
template<class H, class... T> void write(const H& h, const T&... t) { 
    write(h);
    write(t...);
}
 
void solve() {
    
    ll n;
    read(n);
 
    int a = n, b = n-1;
    cout << 2 << endl;
    fr (i, n-1) {
        cout << a << " " << b <<endl;
        a = ceil((float)(a+b)/2);
        b--;
    }
 
 
}   
 
int main() {
    
    fastio;
    
    //Skipped in presense of online judge.
    #ifndef ONLINE_JUDGE
    freopen("D:/Competitive/inputf.in","r",stdin);
    freopen("D:/Competitive/outputf.in","w",stdout);
    #endif
    
    int t(1);
    cin >> t;
 
    frj(i, 1, t+1) {
        // printCase(i);
        solve();
    }
    
    return 0;
    
}