#include <bits/stdc++.h>   using namespace std;   int t, n;   int a[200004];   int main() {     cin >> t;     while (t--) {       cin >> n;       for (int i = 0; i < 2 * n; i++) cin >> a[i];       sort(a, a + 2 * n);       cout << a[n] - a[n - 1] <<   n ;     }     cin >> t;     return 0;   }   