codechef VOTERS - "discrepancies in the voters list" solution

codechef VOTERS - "discrepancies in the voters list": http://www.codechef.com/problems/VOTERS

codechef VOTERS - "discrepancies in the voters list" solution: http://ideone.com/Y5Wz76

#include <iostream>
using namespace std;

int main() {
// your code goes here
long long n1, n2, n3, arr[1000000], k, count=0, n;
cin>>n1>>n2>>n3; n=n1+n2+n3;
for(int i=0; i<1000000; i++) arr[i]=0;
while(n--) {cin>>k; arr[k]++;}
for(int i=0; i<1000000; i++) if(arr[i]>1) count++;
cout<<count<<endl;
for(int i=0; i<1000000; i++) if(arr[i]>1) cout<<i<<endl;
return 0;
}

codechef VOTERS - "discrepancies in the voters list" guidance: 

assume the every ID in the list ranges 0<ID<1000000. and also dont forget that not 0<ID<50000, it is 0<n1<50000, 0<n2<50000 and 0<n3<50000. imho, that is all