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.util.*;
  import java.io.*;
  import java.lang.*;
  
  // Problem - Multiples of 3 onn codeforces MNedium difficulty level 
  // or check on youtube channel CodeNCode
  
  public class Problem {
      // static int Mod = 1000000007;
      static int Mod = 998244353;
      static long dp[][];
      static int g[][];
      static long M= 998244353;
  
      public static void main(String[] args) {
          MyScanner scan = new MyScanner();
          PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));
           int t = scan.nextInt();
          // int t = 1;
          while (t-- > 0) {
            int n= scan.nextInt();
            long h= scan.nextLong();
            long a[]= new long[n];
            for(int i=0;i<n;i++){
                a[i]=scan.nextLong();
            }
           
            long start=0;
            long end=1000000000000000000l;
            long ans=-1;
            while(start<=end){
                long mid= start + (end-start)/2;
                if(solve(mid,a)>=h){
                    ans=mid;
                    end=mid-1;
                }else start=mid+1;
            }
  
            out.println(ans);
  
          }
  
          out.close();
      }
  
  
      static long solve(long mid,long a[]){
         long count=0;
         for(int i=0;i<a.length-1;i++){
             if(a[i+1]-a[i]<=mid) count+= a[i+1]-a[i];
             else count+=mid;
         }
         count+=mid;
         return count;
      }
  
  
      static ArrayList<Integer> digits(int n){
          ArrayList<Integer> list= new ArrayList<>();
          while(n>0){
              list.add(n%10);
              n=n/10;
          }
          Collections.reverse(list);
          return list;
      }
  
      static class Pair {
          int l;
          int r;
  
          Pair(int l, int r) {
              this.l = l;
              this.r = r;
          }
  
          @Override
          public int hashCode() {
              final int prime = 31;
              int result = 1;
              result = prime * result + l;
              result = prime * result + r;
              return result;
          }
  
          @Override
          public boolean equals(Object obj) {
              if (this == obj)
                  return true;
              if (obj == null)
                  return false;
              if (getClass() != obj.getClass())
                  return false;
              Pair other = (Pair) obj;
              if (l != other.l)
                  return false;
              if (r != other.r)
                  return false;
              return true;
          }
  
          @Override
          public String toString() {
              return "Pair [l=" + l + ", r=" + r + "]";
          }
  
      }
  
      public static void reverse(int a[]) {
          int n = a.length;
          for (int i = 0; i < n / 2; i++) {
              int temp = a[i];
              a[i] = a[n - i - 1];
              a[n - i - 1] = temp;
          }
      }
  
      public static void sort(int[] array) {
          ArrayList<Integer> copy = new ArrayList<>();
          for (Integer i : array)
              copy.add(i);
          Collections.sort(copy);
          for (int i = 0; i < array.length; i++)
              array[i] = copy.get(i);
      }
  
      public static void sort(long[] array) {
          ArrayList<Long> copy = new ArrayList<>();
          for (Long i : array)
              copy.add(i);
          Collections.sort(copy);
          for (int i = 0; i < array.length; i++)
              array[i] = copy.get(i);
      }
  
      public static long gcd(long a, long b) {
          if (b == 0)
              return a;
          return gcd(b, a % b); // gcd(a,b) = gcd(a-b,b) or gcd(a,b) = gcd(b,a%b) where a>b
      }
  
      public static int gcd(int a, int b) {
          if (b == 0)
              return a;
          return gcd(b, a % b); // gcd(a,b) = gcd(a-b,b) or gcd(a,b) = gcd(b,a%b) where a>b
      }
  
      public static long lcm(long a, long b) {
          return (a / gcd(a, b)) * b;
      }
  
      static long power(long x, long y) {
          long temp;
          if (y == 0) // a^b= (a^b/2)^2 if b is even
              return 1; // = (a*a^(b-1)) if b is odd
          temp = power(x, y / 2);
          if (y % 2 == 0)
              return temp * temp;
          else
              return x * temp * temp;
      }
  
      static long mod(long x) {
          return ((x % Mod + Mod) % Mod);
      }
  
      static long add(long a, long b) {
          return mod(mod(a) + mod(b));
      }
  
      static int mod(int x) {
          return ((x % Mod + Mod) % Mod);
      }
  
      static int add(int a, int b) {
          return mod(mod(a) + mod(b));
      }
  
      static int sub(int a, int b) {
          return mod(mod(a) - mod(b) + Mod);
      }
  
      static long mul(long a, long b) {
          return mod(mod(a) * mod(b));
      }
  
      static long pow(long x, long y, long p) {
          long res = 1; // Initialize result
          x = x % p; // Update x if it is more than or equal to p
  
          if (x == 0)
              return 0; // In case x is divisible by p;
  
          while (y > 0) {
              // If y is odd, multiply x with result
              if ((y & 1) != 0)
                  res = (res * x) % p;
  
              // y must be even now
              y = y >> 1; // y = y/2
              x = (x * x) % p;
          }
          return res;
      }
  
      static long modInverse(long a, long m) {
          // int g = gcd(a, m);
          // if (g != 1)
          // System.out.println("Inverse doesn't exist");
          // else {
          // // If a and m are relatively prime, then modulo
          // // inverse is a^(m-2) mode m
          // return power(a, m - 2, m);
          // }
          return pow(a, m - 2, m);
      }
  
  }
  
  class MyScanner {
      BufferedReader br;
      StringTokenizer st;
  
      public MyScanner() {
          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;
      }
  
  }
  