Common elements in 3 sorted vectors with extra space, C++ (gcc)

Common elements in 3 sorted vectors with extra space

#include <bits/stdc++.h>
using namespace std;

// } Driver Code Ends

class Solution
{
    public:    
       vector <int> commonElements (int a[], int b[], int c[], int n1, int n2, int n3)
        {
            //code here.
            vector<int>v;
            set<int>s;
            int i=0;int j=0;int k=0;
            int c1=0;
            while(i<n1 && j<n2 && k<n3)
            {
                if(a[i]==b[j] && a[i]==c[k])
                {
                    
                    
                    
                   s.insert(a[i]);
                    i++,j++,k++;
                    
                }
                else if(a[i]<=b[j] && a[i]<=c[k])
                {
                    i++;
                  
                }
                else if(c[k]<=b[j] && c[k]<=a[i])
                {
                    k++; 
                    
                    
                }
                else if(b[j]<=a[i] && b[j]<=c[k])
                {
                    j++;
                    
                }
            }
            for(auto it=s.begin();it!=s.end();it++)
            {
                v.push_back(*it);
            }
            return v;
        }

};

// { Driver Code Starts.

int main ()
{
    int t; cin >> t;
    while (t--)
    {
        int n1, n2, n3; 
        cin >> n1 >> n2 >> n3;
        int A[n1];
        int B[n2];
        int C[n3];
        
        for (int i = 0; i < n1; i++) cin >> A[i];
        for (int i = 0; i < n2; i++) cin >> B[i];
        for (int i = 0; i < n3; i++) cin >> C[i];
        
        Solution ob;
        
        vector <int> res = ob.commonElements (A, B, C, n1, n2, n3);
        if (res.size () == 0) 
            cout << -1;
        for (int i = 0; i < res.size (); i++) 
            cout << res[i] << " "; 
        cout << endl;
    }
}  // } Driver Code Ends


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