1183B - Equalize Prices

#include <iostream>

#include<vector>

#include<string>

#include<math.h>

#include<set>

#include<map>

#include<list>

#include<stack>

#include<queue>

#include <fstream>

#include<iterator>

#include<algorithm>

#include <iomanip>      // std::setprecision

/* ==================================================

  |                                                  |

  |    Author: *** S. M. Sabiul Hajjaj Sabit ***     |

  |       Last Edit:  May,14,2019                    |

   ================================================== */

///***global declaration***///

#define all(arr) arr.begin(),arr.end()

#define pb push_back

#define lb lower_bound

#define up upper_bound

#define sz(x) x.size()

#define min3(a,b,c)  min(min(a,b),c)

#define max3(a,b,c)  max(max(a,b),c)

using namespace std;

int i,j,n,m,sum=0,ans=0;

template <typename T>long long int power(T a, T b)

{

    long long int pow=1;

    for(int i=0; i<b; i++)

        pow *= a;

    return pow;

}

///*********Write Code From Here*********///

int main()

{

    int q,n,k;

    cin>>q;

    for(int i=0; i<q; i++)

    {

        cin>>n>>k;

        int flag=0;

        vector <int> arr;

        for(int i=0; i<n; i++)

        {

            int t;

            cin>>t;

            arr.pb(t);

        }

        sort(all(arr));

        int low=arr[0];

        int high = arr[sz(arr)-1];

        int ans  = low +k;

        if(abs(high- ans) > k) ans =-1;

        cout<<ans<<endl;

    }

}