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.lang.*;
  import java.io.*;
  
  public class Main {
      public static long mod = 1000000007;
  
      public static void main(String[] args) throws java.lang.Exception {
          // your code goes here
          Reader sc = new Reader();
  //        FastNum in = new FastNum(System.in);
          PrintWriter out = new PrintWriter(System.out);
  
          int tests = sc.nextInt();
  
          for (int test = 1; test <= tests; test++) {
              int n = sc.nextInt();
              long h = sc.nextLong();
              long[] arr = new long[n];
              for (int i = 0; i < n; i++) {
                  arr[i] = sc.nextLong();
              }
              if(n==1) {
                  out.println(h);
                  continue;
              }
              if (n >= h) {
                  out.println(1);
                  continue;
              }
              long[] d = new long[n-1];
              for (int i = 0; i < n-1; i++) {
                  d[i] = arr[i+1] - arr[i];
              }
              long start = h / n;
              long end = h;
              long ans = h;
              while (start <= end) {
                  long mid = (start + end) / 2;
                  boolean f = check(d, mid, h);
                  if (f) {
                      ans = Math.min(ans, mid);
                      end = mid - 1;
                  } else {
                      start = mid + 1;
                  }
              }
              out.println(ans);
          }
  
          out.flush();
      }
  
      static boolean check(long[] d, long k, long h) {
          long sum = 0;
          for (int i = 0; i < d.length; i++) {
              sum += Math.min(d[i], k);
          }
          sum += k;
          return sum >= h;
      }
  
      public static long power(long a, long b) {
          if (b == 0)
              return 1;
          long answer = power(a, b / 2) % mod;
          answer = (answer * answer) % mod;
          if (b % 2 != 0)
              answer = (answer * a) % mod;
          return answer;
      }
  
      public static void swap(int x, int y) {
          int t = x;
          x = y;
          y = t;
      }
  
      public static long min(long a, long b) {
          if (a < b) return a;
          return b;
      }
  
      public static long divide(long a, long b) {
          return (a % mod * (power(b, mod - 2) % mod)) % mod;
      }
  
      public static long nCr(long n, long r) {
          long answer = 1;
          long k = min(r, n - r);
          for (long i = 0; i < k; i++) {
              answer = (answer % mod * (n - i) % mod) % mod;
              answer = divide(answer, i + 1);
          }
          return answer % mod;
      }
  
      public static boolean plaindrome(String str) {
          StringBuilder sb = new StringBuilder();
          sb.append(str);
          return (str.equals((sb.reverse()).toString()));
      }
  
      public static class Pair {
          int a;
          int b;
  
          Pair(int s, int e) {
              a = s;
              b = e;
          }
      }
  
      static class Assert {
          static void check(boolean e) {
              if (!e) {
                  throw new AssertionError();
              }
          }
      }
  
  //    static class FastNum implements AutoCloseable {
  //
  //        InputStream is;
  //        byte buffer[] = new byte[1 << 16];
  //        int size = 0;
  //        int pos = 0;
  //
  //        FastNum(InputStream is) {
  //            this.is = is;
  //        }
  //
  //        int nextChar() {
  //            if (pos >= size) {
  //                try {
  //                    size = is.read(buffer);
  //                } catch (IOException e) {
  //                    throw new IOError(e);
  //                }
  //                pos = 0;
  //                if (size == -1) {
  //                    return -1;
  //                }
  //            }
  //            Assert.check(pos < size);
  //            int c = buffer[pos] & 0xFF;
  //            pos++;
  //            return c;
  //        }
  //
  //        int nextInt() {
  //            int c = nextChar();
  //            while (c == ' ' || c == '\r' || c == '\n' || c == '\t') {
  //                c = nextChar();
  //            }
  //            if (c == '-') {
  //                c = nextChar();
  //                Assert.check('0' <= c && c <= '9');
  //                int n = -(c - '0');
  //                c = nextChar();
  //                while ('0' <= c && c <= '9') {
  //                    int d = c - '0';
  //                    c = nextChar();
  //                    Assert.check(n > Integer.MIN_VALUE / 10
  //                            || n == Integer.MIN_VALUE / 10 && d <= -(Integer.MIN_VALUE % 10));
  //                    n = n * 10 - d;
  //                }
  //                return n;
  //            } else {
  //                Assert.check('0' <= c && c <= '9');
  //                int n = c - '0';
  //                c = nextChar();
  //                while ('0' <= c && c <= '9') {
  //                    int d = c - '0';
  //                    c = nextChar();
  //                    Assert.check(
  //                            n < Integer.MAX_VALUE / 10 || n == Integer.MAX_VALUE / 10 && d <= Integer.MAX_VALUE % 10);
  //                    n = n * 10 + d;
  //                }
  //                return n;
  //            }
  //        }
  //
  //        @Override
  //        public void close() {
  //        }
  //    }
  
  
      static class Reader {
          final private int BUFFER_SIZE = 1 << 16;
          private final DataInputStream din;
          private final byte[] buffer;
          private int bufferPointer, bytesRead;
  
          public Reader() {
              din = new DataInputStream(System.in);
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public Reader(String file_name) throws IOException {
              din = new DataInputStream(new FileInputStream(file_name));
              buffer = new byte[BUFFER_SIZE];
              bufferPointer = bytesRead = 0;
          }
  
          public String readLine() throws IOException {
              byte[] buf = new byte[64]; // line length
              int cnt = 0, c;
              while ((c = read()) != -1) {
                  if (c == '\n')
                      break;
                  buf[cnt++] = (byte) c;
              }
              return new String(buf, 0, cnt);
          }
  
          public int nextInt() throws IOException {
              int ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              } while ((c = read()) >= '0' && c <= '9');
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          public long nextLong() throws IOException {
              long ret = 0;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
              do {
                  ret = ret * 10 + c - '0';
              }
              while ((c = read()) >= '0' && c <= '9');
              if (neg)
                  return -ret;
              return ret;
          }
  
          public double nextDouble() throws IOException {
              double ret = 0, div = 1;
              byte c = read();
              while (c <= ' ')
                  c = read();
              boolean neg = (c == '-');
              if (neg)
                  c = read();
  
              do {
                  ret = ret * 10 + c - '0';
              }
              while ((c = read()) >= '0' && c <= '9');
  
              if (c == '.') {
                  while ((c = read()) >= '0' && c <= '9') {
                      ret += (c - '0') / (div *= 10);
                  }
              }
  
              if (neg)
                  return -ret;
              return ret;
          }
  
          private void fillBuffer() throws IOException {
              bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
              if (bytesRead == -1)
                  buffer[0] = -1;
          }
  
          private byte read() throws IOException {
              if (bufferPointer == bytesRead)
                  fillBuffer();
              return buffer[bufferPointer++];
          }
  
          public void close() throws IOException {
              if (din == null)
                  return;
              din.close();
          }
      }
  }
  