Get key from a HashMap using the value [duplicate]

Answer 1

We can get KEY from VALUE. Below is a sample code_

 public class Main {
  public static void main(String[] args) {
    Map map = new HashMap();
    map.put("key_1","one");
    map.put("key_2","two");
    map.put("key_3","three");
    map.put("key_4","four");

    System.out.println(getKeyFromValue(map,"four"));
  }
  public static Object getKeyFromValue(Map hm, Object value) {
    for (Object o : hm.keySet()) {
      if (hm.get(o).equals(value)) {
        return o;
      }
    }
    return null;
  }
}

I hope this will help everyone.

Answer 2

If you are not bound to use Hashmap, I would advise to use pair< T,T >. The individual elements can be accessed by first and second calls.

Have a look at this http://www.cplusplus.com/reference/utility/pair/

I used it here : http://codeforces.com/contest/507/submission/9531943