Problem:
Score : 300 points

Problem Statement

Takahashi made N problems for competitive programming.
The problems are numbered 1 to N, and the difficulty of Problem i is represented as an integer d_i (the higher, the harder).

He is dividing the problems into two categories by choosing an integer K, as follows:

A problem with difficulty K or higher will be for ARCs.

A problem with difficulty lower than K will be for ABCs.

How many choices of the integer K make the number of problems for ARCs and the number of problems for ABCs the same?

Problem Statement

2 \leq N \leq 10^5

N is an even number.

1 \leq d_i \leq 10^5

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
d_1 d_2 ... d_N

Output

Print the number of choices of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 1

6
9 1 4 4 6 7

Sample Output 1

2

If we choose K=5 or 6, Problem 1, 5, and 6 will be for ARCs, Problem 2, 3, and 4 will be for ABCs, and the objective is achieved.
Thus, the answer is 2.

Sample Input 2

8
9 1 14 5 5 4 4 14

Sample Output 2

0

There may be no choice of the integer K that make the number of problems for ARCs and the number of problems for ABCs the same.

Sample Input 3

14
99592 10342 29105 78532 83018 11639 92015 77204 30914 21912 34519 80835 100000 1

Sample Output 3

42685

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.stream.IntStream;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UncheckedIOException;
import java.nio.charset.Charset;
import java.util.StringTokenizer;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.BufferedReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author mikit
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        LightScanner in = new LightScanner(inputStream);
        LightWriter out = new LightWriter(outputStream);
        CDivideTheProblems solver = new CDivideTheProblems();
        solver.solve(1, in, out);
        out.close();
    }

    static class CDivideTheProblems {
        public void solve(int testNumber, LightScanner in, LightWriter out) {
            // out.setBoolLabel(LightWriter.BoolLabel.YES_NO_FIRST_UP);
            int n = in.ints();
            int[] d = in.ints(n);
            IntroSort.sort(d);
            out.ans(d[n / 2] - d[n / 2 - 1]).ln();
        }

    }

    static class LightWriter implements AutoCloseable {
        private final Writer out;
        private boolean autoflush = false;
        private boolean breaked = true;

        public LightWriter(Writer out) {
            this.out = out;
        }

        public LightWriter(OutputStream out) {
            this(new BufferedWriter(new OutputStreamWriter(out, Charset.defaultCharset())));
        }

        public LightWriter print(char c) {
            try {
                out.write(c);
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter print(String s) {
            try {
                out.write(s, 0, s.length());
                breaked = false;
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
            return this;
        }

        public LightWriter ans(String s) {
            if (!breaked) {
                print(' ');
            }
            return print(s);
        }

        public LightWriter ans(int i) {
            return ans(Integer.toString(i));
        }

        public LightWriter ln() {
            print(System.lineSeparator());
            breaked = true;
            if (autoflush) {
                try {
                    out.flush();
                } catch (IOException ex) {
                    throw new UncheckedIOException(ex);
                }
            }
            return this;
        }

        public void close() {
            try {
                out.close();
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
        }

    }

    static class QuickSort {
        private QuickSort() {
        }

        private static void med(int[] a, int low, int x, int y, int z) {
            if (a[z] < a[x]) {
                ArrayUtil.swap(a, low, x);
            } else if (a[y] < a[z]) {
                ArrayUtil.swap(a, low, y);
            } else {
                ArrayUtil.swap(a, low, z);
            }
        }

        static int step(int[] a, int low, int high) {
            int x = low + 1, y = low + (high - low) / 2, z = high - 1;
            if (a[x] < a[y]) {
                med(a, low, x, y, z);
            } else {
                med(a, low, y, x, z);
            }

            int lb = low + 1, ub = high;
            while (true) {
                while (a[lb] < a[low]) {
                    lb++;
                }
                ub--;
                while (a[low] < a[ub]) {
                    ub--;
                }
                if (lb >= ub) {
                    return lb;
                }
                ArrayUtil.swap(a, lb, ub);
                lb++;
            }
        }

    }

    static class LightScanner {
        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public LightScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
        }

        public String string() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int ints() {
            return Integer.parseInt(string());
        }

        public int[] ints(int length) {
            return IntStream.range(0, length).map(x -> ints()).toArray();
        }

    }

    static final class BitMath {
        private BitMath() {
        }

        public static int count(int v) {
            v = (v & 0x55555555) + ((v >> 1) & 0x55555555);
            v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
            v = (v & 0x0f0f0f0f) + ((v >> 4) & 0x0f0f0f0f);
            v = (v & 0x00ff00ff) + ((v >> 8) & 0x00ff00ff);
            v = (v & 0x0000ffff) + ((v >> 16) & 0x0000ffff);
            return v;
        }

        public static int msb(int v) {
            if (v == 0) {
                throw new IllegalArgumentException("Bit not found");
            }
            v |= (v >> 1);
            v |= (v >> 2);
            v |= (v >> 4);
            v |= (v >> 8);
            v |= (v >> 16);
            return count(v) - 1;
        }

    }

    static class IntroSort {
        private static int INSERTIONSORT_THRESHOLD = 16;

        private IntroSort() {
        }

        static void sort(int[] a, int low, int high, int maxDepth) {
            while (high - low > INSERTIONSORT_THRESHOLD) {
                if (maxDepth-- == 0) {
                    HeapSort.sort(a, low, high);
                    return;
                }
                int cut = QuickSort.step(a, low, high);
                sort(a, cut, high, maxDepth);
                high = cut;
            }
            InsertionSort.sort(a, low, high);
        }

        public static void sort(int[] a) {
            if (a.length <= INSERTIONSORT_THRESHOLD) {
                InsertionSort.sort(a, 0, a.length);
            } else {
                sort(a, 0, a.length, 2 * BitMath.msb(a.length));
            }
        }

    }

    static class InsertionSort {
        private InsertionSort() {
        }

        static void sort(int[] a, int low, int high) {
            for (int i = low; i < high; i++) {
                for (int j = i; j > low && a[j - 1] > a[j]; j--) {
                    ArrayUtil.swap(a, j - 1, j);
                }
            }
        }

    }

    static final class ArrayUtil {
        private ArrayUtil() {
        }

        public static void swap(int[] a, int x, int y) {
            int t = a[x];
            a[x] = a[y];
            a[y] = t;
        }

    }

    static class HeapSort {
        private HeapSort() {
        }

        private static void heapfy(int[] a, int low, int high, int i, int val) {
            int child = 2 * i - low + 1;
            while (child < high) {
                if (child + 1 < high && a[child] < a[child + 1]) {
                    child++;
                }
                if (val >= a[child]) {
                    break;
                }
                a[i] = a[child];
                i = child;
                child = 2 * i - low + 1;
            }
            a[i] = val;
        }

        static void sort(int[] a, int low, int high) {
            for (int p = (high + low) / 2 - 1; p >= low; p--) {
                heapfy(a, low, high, p, a[p]);
            }
            while (high > low) {
                high--;
                int pval = a[high];
                a[high] = a[low];
                heapfy(a, low, high, low, pval);
            }
        }

    }
}