Codeforces Global Round 19 1637C - Andrew and Stones Solution

 

Solution in C++: 

///La ilaha illellahu muhammadur rasulullah

///******Bismillahir-Rahmanir-Rahim******///

///Abul Hasnat  Tonmoy

///Department of CSE,23rd batch

///Islamic University,Bangladesh

#include <bits/stdc++.h>

using namespace std;

int main()

{

    ios::sync_with_stdio(false);

    cin.tie(0);

    long long t,n,i,odd,ocnt;

    cin>>t;

    while(t--)

    {

        odd=0;

        ocnt=0;

        cin>>n;

        long long a[n+9];

        for(i=0; i<n; i++)

            cin>>a[i];

        for(i=1; i<n-1; i++)

        {

            ocnt+=a[i]/2;

            if(a[i]%2==1)

                odd++;

        }

        if(ocnt==0)cout<<"-1"<<endl;

        else if((n==3)&&(a[1]%2==1))cout<<"-1"<<endl;

        else cout<<ocnt+odd<<endl;

    }

    return 0;

}