AssigningtoClasses.cpp

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

int main() {

	int t;
	cin >> t;

	while(t--) {
		int n;
	 	cin >> n;

	 	n *= 2;

	 	vector<int> v(n);

	 	for(int i=0;i<n;i++) {
	 		cin >> v[i];
	 	}

	 	sort(v.begin(), v.end());

	 	cout << v[n/2] - v[n/2 - 1] << endl;
	}
	
	return 0;
}