CONSTRUCT (CSP TST 2022-2023)

#define task "CONSTRUCT"

#include <iostream>
#include <cstdio>
#include <iomanip>
#include <cassert>

using namespace std;

using ll = long long;
using ld = long double;

constexpr int N = 1e5 + 5;
int n;
ll x[N], y[N];
ld a[N], b[N];

void Read()
{
    cin >> n;

    for (int i = 1; i <= n; ++i)
        cin >> x[i] >> y[i];
}

ld SolveEquation(ll c1, ll c2)
{
    // assert(!((c1 + c2) & 1));
    return (ld)1.0 * (c1 + c2) / 2;
}

void Cal(ll x[N], ld a[N], int n)
{
    ll tmp = 0;

    for (int i = 1; i < n; ++i)
        if (i & 1)
            tmp = tmp + x[i] * 2;
        else
            tmp = tmp - x[i] * 2;

    a[1] = SolveEquation(x[n] * 2, tmp);

    for (int i = 2; i <= n; ++i)
        a[i] = x[i - 1] * 2 - a[i - 1];
}

void Constrain_4(ll x[N], ld a[N])
{
    ld I2 = (x[1] + x[2]) / 2.0,
       I3 = (x[2] + x[3]) / 2.0,
       I4 = (x[3] + x[4]) / 2.0,
       I1 = (x[4] + x[1]) / 2.0,
       I = (x[1] + x[3]) / 2.0;

    // a_1 + I = 2I1 => a_1 = 2I1 - I

    a[1] = 2 * I1 - I;
    a[2] = 2 * I2 - I;
    a[3] = 2 * I3 - I;
    a[4] = 2 * I4 - I;
}

void Solve()
{
    if (n == 4)
    {
        Constrain_4(x, a);
        Constrain_4(y, b);

        for (int i = 1; i <= n; ++i)
            cout << fixed << setprecision(2) << a[i] << " " << b[i] << "\n";
    }
    else
    {
        Cal(x, a, n);
        Cal(y, b, n);

        for (int i = 1; i <= n; ++i)
            cout << fixed << setprecision(2) << a[i] << " " << b[i] << "\n";
    }
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    if (fopen(task ".INP", "r"))
    {
        freopen(task ".INP", "r", stdin);
        freopen(task ".OUT", "w", stdout);
    }

    Read();
    Solve();
}