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;
using System.Collections.Generic;

namespace 練習問題
{
    class Program {
        static void Main(string[] args) {
            List<int> pattern = new List<int>();
            // int a = 0;
            // int b = 0;
            int c = 0;
            string[] input;
            // int inputCount = 0;
            debug Debug = new debug();
            // Console.WriteLine(args.Length);
            if (args.Length == 0){
                Debug.FlagFalse();
                c = int.Parse(Console.ReadLine());
                input = Console.ReadLine().Split(' ');
                // a = int.Parse(input[0]);
                // b = int.Parse(input[1]);
                // string d = Console.ReadLine();
                //string[] input = Console.ReadLine().Split(' ');
            } else {
                Debug.FlagTrue();
                if (args[0] == "1") {
                    pattern.Add(2);
                    input = new string[2] {"3","1"};
                    c = pattern[0];
                    // Debug.Log(input);
                } else if (args[0] == "2") {
                    pattern.Add(3);
                    input = new string[3] {"2","7","4"};
                    c = pattern[0];
                } else if (args [0] == "3") {
                    pattern.Add(4);
                    input = new string[4] {"20","18","2","18"};
                    c = pattern[0];
                } else {
                    pattern.Add(4);
                    input = new string[4] {"20","18","2","18"};
                    c = pattern[0];
                }
            }
            // Debug.Log(input);
            List<int> SortTarget = new List<int>();
            int Alice = 0;
            int Bob = 0;
            for (int i = 0; i < input.Length; i++) {
                SortTarget.Add(int.Parse(input[i]));
            }
            SortTarget.Sort();
            for (int i = 0; i < input.Length; i++) {
                if ((SortTarget.Count - i) % 2 == 1){
                    Alice += SortTarget[i];
                } else {
                    Bob += SortTarget[i];
                }
            }
            Console.WriteLine(Alice - Bob);
        }

        static int intPow(int target,int kaisu){
            int startTarget = target;
            for (int i = 1; i < kaisu; i++)
            {
                target *= startTarget;
            }
            return target;
        }

        static void bubble_sort(List<List<int>> a) {
            int count=0;
            for (int i = 0; i < a.Count; i++) {
                for (int j = 0; j < a.Count-i-1; j++) {
                    // if (a[j] == a[a.Count - 1]){
                    //     continue;
                    // }
                    count++;
                    if (a[j][1] > a[j+1][1]){
                        int localsave = 0;
                        localsave = a[j+1][1];
                        a[j+1][1] = a[j][1];
                        a[j][1] = localsave;
                        localsave = a[j][0];
                        a[j][0] = a[j+1][0];
                        a[j+1][0] = localsave;
                    }
                }
                //debug(a,"途中" + i);
            }
            // debug(a,"result");
            //Console.WriteLine("回数"+count);
            for (int i = 0; i < a.Count; i++)
            {
                Console.WriteLine(a[i][0]+" "+a[i][1]);
            }
        }
        /* 標準入力と標準出力が使えるかのチェック
        static void echo() {
            string echotest = Console.ReadLine();
            Console.WriteLine(echotest);
        }

        static void HelloWorld(){
            Console.WriteLine("Hello World!");
        }
        */
    }

    public class debug{ //宣言時は、「 debug Debug = new debug(); 」推奨
        bool debug_flag = true;
        public void Log(string str){
            if (debug_flag == true){
                Console.WriteLine(str);
            }
        }
        public void Log(int str){
            if (debug_flag == true){
                Console.WriteLine(str);
            }
        }
        public void Log(float str){
            if (debug_flag == true){
                Console.WriteLine(str);
            }
        }
        public void Log(object obj){
            if (debug_flag == true){
                Console.WriteLine(obj);
            }
        }

        public void Log(int[] arr){
            if (debug_flag == true){
                Console.WriteLine(string.Join(",", arr));
            }
        }
        public void Log(string[] arr){
            if (debug_flag == true){
                Console.WriteLine(string.Join(",", arr));
            }
        }
        public void Log(List<int> arr){
            if (debug_flag == true){
                string shuturyoku = "";
                for (int i = 0; i < arr.Count; i++) {
                    shuturyoku += arr[i] + ",";
                }
                Console.WriteLine(shuturyoku.TrimEnd(','));
            }
        }

        public void Log(List<string> arr){
            if (debug_flag == true){
                string shuturyoku = "";
                for (int i = 0; i < arr.Count; i++) {
                    shuturyoku += arr[i] + ",";
                }
                Console.WriteLine(shuturyoku.TrimEnd(','));
            }
        }

        public void Log(List<float> arr){
            if (debug_flag == true){
                string shuturyoku = "";
                for (int i = 0; i < arr.Count; i++) {
                    shuturyoku += arr[i] + ",";
                }
                Console.WriteLine(shuturyoku.TrimEnd(','));
            }
        }
        public void Log(){
            if (debug_flag == true){
                Console.WriteLine("アタイイレナサイ");
            }
        }
        public void FlagFalse(){
            debug_flag = false;
        }
        public void FlagTrue(){
            debug_flag = true;
        }
    }
}