Problem:
Score : 300 points

Problem Statement

There are N cities on a number line. The i-th city is located at coordinate x_i.

Your objective is to visit all these cities at least once.

In order to do so, you will first set a positive integer D.

Then, you will depart from coordinate X and perform Move 1 and Move 2 below, as many times as you like:

Move 1: travel from coordinate y to coordinate y + D.

Move 2: travel from coordinate y to coordinate y - D.

Find the maximum value of D that enables you to visit all the cities.

Here, to visit a city is to travel to the coordinate where that city is located.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq X \leq 10^9

1 \leq x_i \leq 10^9

x_i are all different.

x_1, x_2, ..., x_N \neq X

Input

Input is given from Standard Input in the following format:

N X
x_1 x_2 ... x_N

Output

Print the maximum value of D that enables you to visit all the cities.

Sample Input 1

3 3
1 7 11

Sample Output 1

2

Setting D = 2 enables you to visit all the cities as follows, and this is the maximum value of such D.

Perform Move 2 to travel to coordinate 1.

Perform Move 1 to travel to coordinate 3.

Perform Move 1 to travel to coordinate 5.

Perform Move 1 to travel to coordinate 7.

Perform Move 1 to travel to coordinate 9.

Perform Move 1 to travel to coordinate 11.

Sample Input 2

3 81
33 105 57

Sample Output 2

24

Sample Input 3

1 1
1000000000

Sample Output 3

999999999

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;
import java.util.Arrays;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int offset = Integer.parseInt(scanner.nextLine().split(" ")[1]);
		System.out.println(
				Arrays.stream(scanner.nextLine().split(" "))
					.mapToInt(Integer::parseInt)
					.map(i -> i - offset)
					.map(Math::abs)
					.filter(i -> i != 0)
					.reduce((i1, i2) -> gcd(i1, i2))
					.getAsInt()
				);
	}
	public static int gcd(int i1, int i2) {
		int bg = i1 > i2 ? i1 : i2;
		int sm = i1 > i2 ? i2 : i1;
		int remainder = sm;
		while(bg % sm != 0) {
			remainder = bg % sm;
			bg = sm;
			sm = remainder;
		}
		return remainder;
	}
}