import java.util.*;

public class Main {

    public static void main(String[] args) {

        class IndexedCollection<K, V> extends HashMap<Integer, HashMap<K, V>> {
            public HashMap<V, HashMap<K, ArrayList<Integer>>> indexes = new HashMap<>();
            private int autoIncrementId = 0;

            private int getNextId() {
                return autoIncrementId++;
            }

            public HashMap<K, V> put(HashMap<K, V> e) {
                int id = getNextId();
                for (Map.Entry<K, V> entry : e.entrySet()) {
                    HashMap<K, ArrayList<Integer>> values = indexes.get(entry.getValue());
                    if (values == null) {
                        values = new HashMap<>();
                        indexes.put(entry.getValue(), values);
                    }
                    ArrayList<Integer> ids = values.get(entry.getKey());
                    if (ids == null) {
                        ids = new ArrayList<>();
                        values.put(entry.getKey(), ids);
                    }
                    ids.add(id);
                }
                return super.put(id, e);
            }

            public HashMap<K, V> get(int index) {
                return super.get(index);
            }

            public HashSet<Integer> find(HashMap<K, V> e) {
                HashSet<Integer> result = new HashSet<>();
                for (Map.Entry<K, V> entry : e.entrySet()) {
                    HashMap<K, ArrayList<Integer>> values = indexes.get(entry.getValue());
                    if (values != null) {
                        ArrayList<Integer> ids = values.get(entry.getKey());
                        if (ids != null) {
                            if (result.isEmpty()) {
                                result.addAll(ids);
                            } else {
                                result.retainAll(result);
                            }
                        } else {
                            return new HashSet<>();
                        }
                    } else {
                        return new HashSet<>();
                    }
                }
                return result;
            }
        }

        // test
        IndexedCollection<String, String> collection = new IndexedCollection<>();

        System.out.println("Generating data...");
        Random rn = new Random();
//        for (int i = 0; i < 1000000; i++) {
//            HashMap<String, String> e = new HashMap<>();
//            e.put("field_1", Integer.toString(rn.nextInt(10000)));
//            e.put("field_2", Integer.toString(rn.nextInt(10000)));
//            e.put("field_3", Integer.toString(rn.nextInt(10000)));
//            collection.put(e);
//        }

        {
            HashMap<String, String> e = new HashMap<>();
            e.put("field_1", "value_1");
            e.put("field_2", "value_2");
            e.put("field_3", "value_3");
            collection.put(e);
        }

        HashMap<String, String> e = new HashMap<>();
        e.put("field_1", "value_1");
        e.put("field_2", "value_2");

        HashSet<Integer> result = collection.find(e);
        System.out.println("Found ids: " + result.toString());

        System.out.println("Found data");

        for (int id : result) {
            System.out.println(collection.get(id));
        }

    }
}