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 Go (1.6) (judge verdict: Accepted)

// use goroutine by force
package main

import (
	"fmt"
	"sort"
	"sync"
	//"time"
)

func main() {
	var N int
	fmt.Scan(&N)
	a := make([]int, N)
	for i := range a {
		fmt.Scan(&a[i])
	}

	sort.Sort(sort.Reverse(sort.IntSlice(a)))

	A := 0
	B := 0
	var lock sync.Mutex
	addAlice := func() {
		lock.Lock()
		defer lock.Unlock()
		if len(a) > 0 {
			A += a[0]
			a = a[1:]
		}
	}
	addBob := func() {
		lock.Lock()
		defer lock.Unlock()
		if len(a) > 0 {
			B += a[0]
			a = a[1:]
		}
	}

	startA := make(chan interface{})
	close(startA)
	toA := make(chan int)
	toB := make(chan int)

	terminated := make(chan interface{})
loop:
	for {
		select {
		case <-terminated:
			break loop
		default:
		}

		// wgを使わないとBのgoroutineが起動する前にAが重複して起動する
		var wg sync.WaitGroup
		wg.Add(2)
		go func() {
			wg.Done()
			if len(a) == 0 {
				//fmt.Println("len a == 0")
				close(terminated)
			}
			<-startA
			addAlice()
			//fmt.Printf("A: %d %v\n", A, a)
			toB <- 1
			<-toA
		}()
		go func() {
			wg.Done()
			<-toB
			addBob()
			//fmt.Printf("B: %d %v\n", B, a)
			toA <- 1
		}()
		wg.Wait()
		//time.Sleep(1 * time.Second)
		//time.Sleep(1 * time.Millisecond)
	}

	//fmt.Printf("A: %d B: %d\n", A, B)
	fmt.Println(A - B)
}