ups_and_down.cpp

#include <bits/stdc++.h>
using namespace std;

int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int n;
        cin >> n;
        long long int a[n];
        for (int i = 0; i < n; i++)
            cin >> a[i];
        sort(a, a + n);
        for (int i = 0; i < n - 1; i++)
        {
            if (i % 2 != 0)
            {
                int temp = a[i];
                a[i] = a[i + 1];
                a[i + 1] = temp;
            }
        }
        for (int i = 0; i < n; i++)
            cout << a[i] << " ";
        cout << endl;
    }
    return 0;
}