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 C (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>

void	ft_swap(int *a, int *b)
{
	int tmp;
	
	tmp = *a;
	*a = *b;
	*b = tmp;
}

void	ft_qsort(int *tab, int left, int right)
{
	int Left = left;
	int Right = right;
	int pivot = tab[(left + right) / 2];

	while (1)
	{
		while (tab[Left] < pivot)
			Left++;
		while (tab[Right] > pivot)
			Right--;
		if (Left >= Right)
			break ;
		ft_swap(&tab[Left], &tab[Right]);
		Left++;
		Right--;
	}

	if (Left - 1 > left)
		ft_qsort(tab, left, Left - 1);
	if (Right + 1 < right)
		ft_qsort(tab, Right + 1, right);
}

int		main(void)
{
	int n;
	scanf("%d", &n);
	int tab[n];
	int i = 0;
	while (i < n)
		scanf("%d", &tab[i++]);
	ft_qsort(tab, 0, n - 1);
	int arc = tab[n / 2];
	int abc = tab[(n / 2) - 1];
	printf("%d\n", arc - abc);
	return (0);
}