Language: C++

#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vvvll = std::vector<vvll>;
using dd = double;
using vdd = std::vector<dd>;
using vvdd = std::vector<vdd>;
using vvvdd = std::vector<vvdd>;

constexpr ll INF = 1LL << 60;
//constexpr ll MOD = (ll)(1e9 + 7);// 998244353L;
constexpr dd EPS = 1e-11;

typedef std::numeric_limits< double > dbl;

//cin,cout高速化のおまじない＋桁数指定
struct Fast{
	Fast(){
		cin.tie(0);
		ios::sync_with_stdio(false);
		cout << fixed << setprecision(std::numeric_limits<double>::max_digits10);
	}
} fast;

#define REPS(i, S, E) for (ll i = (S); i <= (E); i++)
#define REP(i, N) REPS(i, 0, N-1)
#define DEPS(i, E, S) for (ll i = (E); i >= (S); i--)
#define DEP(i, N) DEPS(i, N-1, 0)
#define EACH(e, v) for (auto&& e : v)

template<class T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; }return false; }
template<class T> inline T MaxE(vector<T> &v, ll S, ll E){ T m=v[S]; REPS(i, S, E)chmax(m, v[i]); return m; }//v[S]～v[E]の最大値
template<class T> inline T MinE(vector<T> &v, ll S, ll E){ T m=v[S]; REPS(i, S, E)chmin(m, v[i]); return m; }//v[S]～v[E]の最小値
template<class T> inline T MaxE(vector<T> &v, ll N) { return MaxE(v, 0, N - 1); } //先頭N個中の最大値
template<class T> inline T MinE(vector<T> &v, ll N) { return MinE(v, 0, N - 1); }
template<class T> inline T MaxE(vector<T> &v) { return MaxE(v, (ll)v.size()); }
template<class T> inline T MinE(vector<T> &v) { return MinE(v, (ll)v.size()); }
template<class T> inline ll MaxI(vector<T> &v, ll S, ll E){ ll m=S; REPS(i, S, E){ if (v[i]>v[m])m=i; }return m; }
template<class T> inline ll MinI(vector<T> &v, ll S, ll E){ ll m=S; REPS(i, S, E){ if (v[i]<v[m])m=i; }return m; }
template<class T> inline ll MaxI(vector<T> &v, ll N) { return MaxI(v, 0, N - 1); }
template<class T> inline ll MinI(vector<T> &v, ll N) { return MinI(v, 0, N - 1); }
template<class T> inline ll MaxI(vector<T> &v) { return MaxI(v, (ll)v.size()); }
template<class T> inline ll MinI(vector<T> &v) { return MinI(v, (ll)v.size()); }
template<class T> inline T Sum(vector<T> &v, ll S, ll E){ T s=v[S]; REPS(i, S+1, E)s+=v[i]; return s; }
template<class T> inline T Sum(vector<T> &v, ll N) { return Sum(v, 0, N - 1); }
template<class T> inline T Sum(vector<T> &v) { return Sum(v, v.size()); }

template<int mod> struct modll{
	ll val;
	modll(ll v = 0): val(v % mod){
		if (val < 0) val += mod;
	}
	modll operator - () { return -val; }
	modll operator + (modll &b) { return val + b.val; }
	modll operator - (modll &b) {return val - b.val;}
	modll operator * (modll &b) {return val * b.val;}
	modll operator + (ll b) { return *this + modll(b); }
	modll operator - (ll b) { return *this - modll(b); }
	modll operator * (ll b) { return *this * modll(b); }
	modll &operator += (modll &b) { val=(val+b.val)%mod; return *this; }
	modll &operator -= (modll &b) { val=(val+mod-b.val)%mod; return *this; }
	modll &operator *= (modll &b) { val=(val*r.val)%mod; return *this; }
	modll &operator += (ll b) { return *this += modll(b); }
	modll &operator -= (ll b) { return *this -= modll(b); }
	modll &operator *= (ll b) { return *this *= modll(b); }
};

constexpr ll MOD = (ll)(1e9 + 7); // 998244353L;

inline ll AddMOD(ll a, ll b) { return (a + b) % MOD; }
inline ll SubMOD(ll a, ll b) { return (a - b + MOD) % MOD; }
inline ll MulMOD(ll a, ll b) { return (a * b) % MOD; }
template<class T> inline T SumMOD(vector<T> &v, ll S, ll E){ T s=v[S]; REPS(i, S+1, E)s=(s+v[i])%MOD; return s; }
template<class T> inline T SumMOD(vector<T> &v, ll N) { return SumMOD(v, 0, N - 1); }
template<class T> inline T SumMOD(vector<T> &v) { return SumMOD(v, v.size()); }

inline ll in() { ll x; cin >> x; return x; }
inline double inD() { double x; cin >> x; return x; }
inline string inS() { string x; cin >> x; return std::move(x); }
template<class T=ll> inline vector<T> in_v(ll N){ vector<T> v(N); REP(i, N)cin>>v[i]; return move(v); }
inline void To0origin(vll &v) { EACH(e, v) e--; }


ll N;
vll d;

int main()
{
	cin >> N;
	d = in_v(N);
	if (N%2 == 1) {
		cout << 0 << '\n';
		return 0;
	}

	std::sort(d.begin(), d.end());
	cout << d[N/2] - d[N/2-1] << '\n';
	return 0;
#if 0
	modll<11> x;
	x = 1;
	auto y = -x;
	auto z = y + 1;
	//modllの動作確認必要。


	//cout << Tbl(N-1, M-1) << '\n';
#endif
}


Compiler output:
a.cc: In member function 'modll<mod>& modll<mod>::operator*=(modll<mod>&)':
a.cc:65:50: error: 'r' was not declared in this scope
   65 |         modll &operator *= (modll &b) { val=(val*r.val)%mod; return *this; }
      |                                                  ^