description: Monocarp is playing yet another computer game. In this game, his character has to kill a dragon. The battle with the dragon lasts 100^{500} seconds, during which Monocarp attacks the dragon with a poisoned dagger. The i-th attack is performed at the beginning of the a_i-th second from the battle start. The dagger itself does not deal damage, but it applies a poison effect on the dragon, which deals 1 damage during each of the next k seconds (starting with the same second when the dragon was stabbed by the dagger). However, if the dragon has already been poisoned, then the dagger updates the poison effect (i.e. cancels the current poison effect and applies a new one).
  
  For example, suppose k = 4, and Monocarp stabs the dragon during the seconds 2, 4 and 10. Then the poison effect is applied at the start of the 2-nd second and deals 1 damage during the 2-nd and 3-rd seconds; then, at the beginning of the 4-th second, the poison effect is reapplied, so it deals exactly 1 damage during the seconds 4, 5, 6 and 7; then, during the 10-th second, the poison effect is applied again, and it deals 1 damage during the seconds 10, 11, 12 and 13. In total, the dragon receives 10 damage.
  
  Monocarp knows that the dragon has h hit points, and if he deals at least h damage to the dragon during the battle — he slays the dragon. Monocarp has not decided on the strength of the poison he will use during the battle, so he wants to find the minimum possible value of k (the number of seconds the poison effect lasts) that is enough to deal at least h damage to the dragon.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 1000) — the number of test cases.
  
  The first line of the test case contains two integers n and h (1 ≤ n ≤ 100; 1 ≤ h ≤ 10^{18}) — the number of Monocarp's attacks and the amount of damage that needs to be dealt.
  
  The second line contains n integers a_1, a_2, ..., a_n (1 ≤ a_i ≤ 10^9; a_i < a_{i + 1}), where a_i is the second when the i-th attack is performed.
  
  Output
  
  For each test case, print a single integer — the minimum value of the parameter k, such that Monocarp will cause at least h damage to the dragon.
  
  Example
  
  Input
  
  
  4
  2 5
  1 5
  3 10
  2 4 10
  5 3
  1 2 4 5 7
  4 1000
  3 25 64 1337
  
  
  Output
  
  
  3
  4
  1
  470
  
  Note
  
  In the first example, for k=3, damage is dealt in seconds [1, 2, 3, 5, 6, 7].
  
  In the second example, for k=4, damage is dealt in seconds [2, 3, 4, 5, 6, 7, 10, 11, 12, 13].
  
  In the third example, for k=1, damage is dealt in seconds [1, 2, 4, 5, 7].
solution: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.LinkedHashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.StringTokenizer;
  
  public class P1613C {
  	static PrintWriter out = new PrintWriter(System.out);
  	static MyFastReaderP1613C in = new MyFastReaderP1613C();
  	static long mod = (long) (1e9 + 7);
  
  	public static void main(String[] args) throws Exception {
  		int test = i();
  		while (test-- > 0) {
  
  			int n = i();
  			long h = l();
  			long[] arr = arrL(n);
  			sort(arr);
  
  			long l = 1, r = h;
  			long ans = h;
  			while (l <= r) {
  				long mid = (r - l) / 2 + l;
  
  				if (isPossible(arr, mid, h)) {
  
  					ans = Math.min(ans, mid);
  					r = mid - 1;
  				} else
  					l = mid + 1;
  
  			}
  
  			out.print(ans);
  			out.print("\n");
  			out.flush();
  		}
  		out.close();
  	}
  
  	private static boolean isPossible(long[] arr, long mid, long h) {
  
  		long ans = mid;
  
  		for (int i = 0; i < arr.length - 1; i++) {
  
  			if (arr[i] + mid - 1 < arr[i + 1])
  				ans += mid;
  
  			else
  				ans += (arr[i + 1] -arr[i]);
  
  		}
  		return ans >= h ? true : false;
  	}
  
  	static class pair {
  		long x, y;
  
  		pair(long ar, long ar2) {
  			x = ar;
  			y = ar2;
  		}
  	}
  
  	static void sort(long[] a) // check for long
  	{
  		ArrayList<Long> l = new ArrayList<>();
  		for (long i : a)
  			l.add(i);
  		Collections.sort(l);
  		for (int i = 0; i < a.length; i++)
  			a[i] = l.get(i);
  	}
  
  	static void sort(int[] a) {
  		ArrayList<Integer> l = new ArrayList<>();
  		for (int i : a)
  			l.add(i);
  		Collections.sort(l);
  		for (int i = 0; i < a.length; i++)
  			a[i] = l.get(i);
  	}
  
  	public static int gcd(int a, int b) {
  		if (a == 0)
  			return b;
  		return gcd(b % a, a);
  	}
  
  	static class DescendingComparator implements Comparator<Integer> {
  		public int compare(Integer a, Integer b) {
  			return b - a;
  		}
  	}
  
  	static class AscendingComparator implements Comparator<Integer> {
  		public int compare(Integer a, Integer b) {
  			return a - b;
  		}
  	}
  
  	static boolean isPalindrome(char X[]) {
  		int l = 0, r = X.length - 1;
  		while (l <= r) {
  			if (X[l] != X[r])
  				return false;
  			l++;
  			r--;
  		}
  		return true;
  	}
  
  	static long fact(long N) {
  		long num = 1L;
  		while (N >= 1) {
  			num = ((num % mod) * (N % mod)) % mod;
  			N--;
  		}
  		return num;
  	}
  
  	static long pow(long a, long b) {
  		long mod = 1000000007;
  		long pow = 1;
  		long x = a;
  		while (b != 0) {
  			if ((b & 1) != 0)
  				pow = (pow * x) % mod;
  			x = (x * x) % mod;
  			b /= 2;
  		}
  		return pow;
  	}
  
  	static long toggleBits(long x)// one's complement || Toggle bits
  	{
  		int n = (int) (Math.floor(Math.log(x) / Math.log(2))) + 1;
  
  		return ((1 << n) - 1) ^ x;
  	}
  
  	static int countBits(long a) {
  		return (int) (Math.log(a) / Math.log(2) + 1);
  	}
  
  	static boolean isPrime(long N) {
  		if (N <= 1)
  			return false;
  		if (N <= 3)
  			return true;
  		if (N % 2 == 0 || N % 3 == 0)
  			return false;
  		for (int i = 5; i * i <= N; i = i + 6)
  			if (N % i == 0 || N % (i + 2) == 0)
  				return false;
  		return true;
  	}
  
  	static long GCD(long a, long b) {
  		if (b == 0) {
  			return a;
  		} else
  			return GCD(b, a % b);
  	}
  
  	// Debugging Functions Starts
  
  	static void print(char A[]) {
  		for (char c : A)
  			System.out.print(c + " ");
  		System.out.println();
  	}
  
  	static void print(boolean A[]) {
  		for (boolean c : A)
  			System.out.print(c + " ");
  		System.out.println();
  	}
  
  	static void print(int A[]) {
  		for (int a : A)
  			System.out.print(a + " ");
  		System.out.println();
  	}
  
  	static void print(long A[]) {
  		for (long i : A)
  			System.out.print(i + " ");
  		System.out.println();
  
  	}
  
  	static void print(ArrayList<Integer> A) {
  		for (int a : A)
  			System.out.print(a + " ");
  		System.out.println();
  	}
  
  	// Debugging Functions END
  	// ----------------------
  	// IO FUNCTIONS STARTS
  	static HashMap<Integer, Integer> getHashMap(int A[]) {
  		HashMap<Integer, Integer> mp = new HashMap<>();
  		for (int a : A) {
  			int f = mp.getOrDefault(a, 0) + 1;
  			mp.put(a, f);
  		}
  		return mp;
  	}
  
  	public static Map<Character, Integer> mapSortByValue(Map<Character, Integer> hm) {
  		// Create a list from elements of HashMap
  		List<Map.Entry<Character, Integer>> list = new LinkedList<Map.Entry<Character, Integer>>(hm.entrySet());
  
  		// Sort the list
  		Collections.sort(list, new Comparator<Map.Entry<Character, Integer>>() {
  			public int compare(Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2) {
  				return o1.getValue() - o2.getValue();
  			}
  		});
  
  		// put data from sorted list to hashmap
  		Map<Character, Integer> temp = new LinkedHashMap<Character, Integer>();
  		for (Map.Entry<Character, Integer> aa : list) {
  			temp.put(aa.getKey(), aa.getValue());
  		}
  		return temp;
  	}
  
  	static String string() {
  		return in.nextLine();
  	}
  
  	static int i() {
  		return in.nextInt();
  	}
  
  	static long l() {
  		return in.nextLong();
  	}
  
  	static int[] arrI(int N) {
  		int A[] = new int[N];
  		for (int i = 0; i < N; i++) {
  			A[i] = in.nextInt();
  		}
  		return A;
  	}
  
  	static long[] arrL(int N) {
  		long A[] = new long[N];
  		for (int i = 0; i < A.length; i++)
  			A[i] = in.nextLong();
  		return A;
  	}
  
  }
  
  class MyFastReaderP1613C {
  	BufferedReader br;
  	StringTokenizer st;
  
  	public MyFastReaderP1613C() {
  		br = new BufferedReader(new InputStreamReader(System.in));
  	}
  
  	String next() {
  		while (st == null || !st.hasMoreElements()) {
  			try {
  				st = new StringTokenizer(br.readLine());
  			} catch (IOException e) {
  				e.printStackTrace();
  			}
  		}
  		return st.nextToken();
  	}
  
  	int nextInt() {
  		return Integer.parseInt(next());
  	}
  
  	long nextLong() {
  		return Long.parseLong(next());
  	}
  
  	double nextDouble() {
  		return Double.parseDouble(next());
  	}
  
  	String nextLine() {
  		String str = "";
  		try {
  			str = br.readLine();
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  		return str;
  	}
  }
  