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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

// (l, r]
func lowerbound(a []int, k int) int {
	l := -1
	r := len(a)
	for r-l > 1 {
		mid := (l + r) / 2
		if a[mid] >= k {
			r = mid
		} else {
			l = mid
		}
	}
	return r
}

func main() {
	var n int
	fmt.Scan(&n)
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	a := make([]int, n)
	for i := range a {
		sc.Scan()
		a[i], _ = strconv.Atoi(sc.Text())
	}
	sort.Ints(a)
	ans := 0
	for k := 1; k <= a[n-1]; k++ {
		if lowerbound(a, k) == n/2 {
			ans++
		}
	}
	fmt.Println(ans)
}