Problem:
Score: 200 points

Problem Statement

We have N cards. A number a_i is written on the i-th card.

Alice and Bob will play a game using these cards. In this game, Alice and Bob alternately take one card. Alice goes first.

The game ends when all the cards are taken by the two players, and the score of each player is the sum of the numbers written on the cards he/she has taken. When both players take the optimal strategy to maximize their scores, find Alice's score minus Bob's score.

Constraints

N is an integer between 1 and 100 (inclusive).

a_i \ (1 \leq i \leq N) is an integer between 1 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 a_3 ... a_N

Output

Print Alice's score minus Bob's score when both players take the optimal strategy to maximize their scores.

Sample Input 1

2
3 1

Sample Output 1

2

First, Alice will take the card with 3. Then, Bob will take the card with 1.
The difference of their scores will be 3 - 1 = 2.

Sample Input 2

3
2 7 4

Sample Output 2

5

First, Alice will take the card with 7. Then, Bob will take the card with 4. Lastly, Alice will take the card with 2. The difference of their scores will be 7 - 4 + 2 = 5. The difference of their scores will be 3 - 1 = 2.

Sample Input 3

4
20 18 2 18

Sample Output 3

18

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using static System.Console;
using static System.Math;

namespace Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Solve.Answer();
            }
            catch (Exception ex)
            {
                WriteLine(ex.ToString());
            }
        }
    }

    public class Solve
    {
        public static void Answer()
        {
            var n = IO.ReadInt;
            var a = IO.ReadSplitInt;

            a.Sort((x, y) => y - x);
            var ans = 0;
            for (int i = 0; i < n; i += 2)
            {
                ans += a[i];
            }
            for (int i = 1; i < n; i += 2)
            {
                ans -= a[i];
            }
            WriteLine(ans);
        }

        public class IO
        {
            #region Input
            public static string ReadString => ReadLine();
            public static int ReadInt => int.Parse(ReadLine());
            public static long ReadLong => long.Parse(ReadLine());
            public static double ReadDouble => double.Parse(ReadLine());

            public static List<string> ReadSplitString => ReadLine().Split().ToList();
            public static List<int> ReadSplitInt => ReadLine().Split().Select(s => int.Parse(s)).ToList();
            public static List<long> ReadSplitLong => ReadLine().Split().Select(s => long.Parse(s)).ToList();
            public static List<double> ReadSplitdouble => ReadLine().Split().Select(s => double.Parse(s)).ToList();
            #endregion

            #region Output
            public static void OutJoinSpace<T>(IEnumerable<T> list) => WriteLine(string.Join(" ", list));
            public static void WriteLineYes_or_No(bool flag) => WriteLine(flag ? "Yes" : "No");

            #endregion
        }

        public class Mod
        {
            #region
            // 割る数の定義
            private readonly static long M = 1000000007;

            // 足し算
            public static long Add(long a, long b) => (a * b) % M;
            // 引き算
            public static long Sub(long a, long b) => (a - b) % M >= 0 ? (a - b) % M : (a - b) % M + M;
            // 掛け算
            public static long Multi(long a, long b) => (a * b) % M;
            #endregion
        }

        public class Scanner
        {
            #region
            public string Str => Console.ReadLine().Trim();
            public int Int => int.Parse(Str);
            public long Long => long.Parse(Str);
            public double Double => double.Parse(Str);
            public int[] ArrInt => Str.Split(' ').Select(int.Parse).ToArray();
            public long[] ArrLong => Str.Split(' ').Select(long.Parse).ToArray();
            //public char[][] Grid(int n) => Create(n, () => Str.ToCharArray());
            //public int[] ArrInt1D(int n) => Create(n, () => Int);
            //public long[] ArrLong1D(int n) => Create(n, () => Long);
            //public int[][] ArrInt2D(int n) => Create(n, () => ArrInt);
            //public long[][] ArrLong2D(int n) => Create(n, () => ArrLong);
            private Queue<string> q = new Queue<string>();
            [MethodImpl(MethodImplOptions.AggressiveInlining)]
            // インライン化を推奨する
            public T Next<T>()
            {
                if (q.Count == 0) foreach (var item in Str.Split(' ')) q.Enqueue(item);
                return (T)Convert.ChangeType(q.Dequeue(), typeof(T));
            }
            public void Make<T1>(out T1 v1) => v1 = Next<T1>();
            public void Make<T1, T2>(out T1 v1, out T2 v2) { v1 = Next<T1>(); v2 = Next<T2>(); }
            public void Make<T1, T2, T3>(out T1 v1, out T2 v2, out T3 v3) { Make(out v1, out v2); v3 = Next<T3>(); }
            public void Make<T1, T2, T3, T4>(out T1 v1, out T2 v2, out T3 v3, out T4 v4) { Make(out v1, out v2, out v3); v4 = Next<T4>(); }
            public void Make<T1, T2, T3, T4, T5>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5) { Make(out v1, out v2, out v3, out v4); v5 = Next<T5>(); }
            public void Make<T1, T2, T3, T4, T5, T6>(out T1 v1, out T2 v2, out T3 v3, out T4 v4, out T5 v5, out T6 v6) { Make(out v1, out v2, out v3, out v4, out v5); v6 = Next<T6>(); }
            #endregion
        }

        public static long GCD(long x, long y)
        {
            #region
            if (x < y)
            {
                var tmp = x;
                x = y;
                y = tmp;
            }
            while (true)

            {
                if (x % y == 0)
                {
                    return y;
                }
                else
                {
                    var tmp = x;
                    x = y;
                    y = tmp % y;
                }
            }
            #endregion
        }

        public static long Choice2(long n)
        {
            #region
            if (n <= 1)
                return 0;
            if (n == 2)
                return 1;
            else
                return n * (n - 1) / 2;
            #endregion
        }
    }
}