#include "TFile.h"
#include "TTree.h"
#include <iostream>
#include <unordered_set>

using namespace std;

void find_duplicates(const char* filename1, const char* filename2) {
  unordered_set<int> chip_set;
  for (int m = 0; m < 2; ++m) {
    TFile* file = new TFile(m == 0 ? filename1 : filename2);
    TTree* tree = (TTree*) file->Get("tree");
    int chip;
    tree->SetBranchAddress("iChip", &chip);
    int n = tree->GetEntries();
    for (int i = 0; i < n; ++i) {
      tree->GetEntry(i);
      if (!chip_set.insert(chip).second)
	cout << chip << " ";
    }
    delete file;
  }
  cout << endl;
}