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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

void quick_sort(int a[], int first, int last);

int main(void){
  int n;
  scanf("%d", &n);
  int question[n];

  for(int i=0 ; i<n ; i++)
    scanf("%d", &question[i]);

  quick_sort(question, 0, n-1);

  int ans = question[n/2] - question[n/2-1];

  printf("%d\n", ans);

  return 0;
}



void quick_sort(int a[], int first, int last){
  int temp, k;
  int flag=1;
  int p = a[first];
  int i = first, j = last;

  while(flag){
    while(a[i]<p)
      i++;
    while(p<a[j])
      j--;
    if(i<j){
      temp=a[i];
      a[i]=a[j];
      a[j]=temp;
      i++; j--;
    }
    else
      flag=0;
  }

  if(first<i-1)
	quick_sort(a,first,i-1);
  if(j+1<last)
	quick_sort(a,j+1,last);
}