help

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>

using namespace std;

#define MOD 1000000007
#define MOD1 998244353
#define rep(i,b)  for(int i = 0; i < b; i++)
#define nl "\n"
#define sp " "
#define inf 1000000004
#define minf INT_MIN
#define pb push_back
#define vi vector<int>
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define ys cout << "YES" << nl
#define no cout << "NO" << nl
#define ll long long
#define int long long
template<typename T> istream& operator>>(istream& is,  vector<T> &v){for (auto& i : v) is >> i;        return is;}
template<typename T> ostream& operator<<(ostream& os,  vector<T>  v){for (auto& i : v) os << i << ' '; return os;}
vector<int> suffix(vector<int> arr){int n = sz(arr); vector<int> suffixSum(n, 0); suffixSum[n - 1] = arr[n - 1]; for (int i = n - 2; i >= 0; i--) suffixSum[i] = suffixSum[i + 1] + arr[i]; return suffixSum;}

int n , h;

bool helper(vector<int>& v , int k){
  int sum = 0;
  for(int i = 0; i < n - 1; i++){
    sum += min((v[i + 1] - v[i]) , k) + 1;
  }
  sum += (k - 1);
  return sum > h;
}

void solve(){
  cin >> n >> h;
  vi v(n); cin >> v;
  int low = 1, high = 1e18 , ans = 0;
  while(low <= high){
    int mid = low + (high - low) / 2;
    if(helper(v , mid)){
      ans = mid;
      high = mid - 1;
    }
    else low = mid + 1;
  }
  cout << ans << nl;
}

int32_t main(){
  ios_base::sync_with_stdio(0);cin.tie(0);
  int t = 1;
  cin >> t;
  while(t--){
    solve();
  }
  return 0;
}