Problem 4

#include<bits/stdc++.h>
#define int long long int
#define endl '\n'
using namespace std;
int a[200007];
main()
{
    ios::sync_with_stdio(0);cin.tie(0);
    int T;cin>>T;
    while(T--){
        int n;cin>>n;
        for(int i=1;i<=2*n;i++)cin>>a[i];
        sort(a+1,a+2*n+1);
        cout<<a[n+1]-a[n]<<endl;
    }
}