Find out whether two HashSets have a duplicate value

Question

I need a function like the following,

boolean hasDuplicateValue(HashSet hs1, HashSet hs2) {        
    // return false;
}

This thread Efficiently finding the intersection of a variable number of sets of strings discusses a similar issue, however in this thread they also need the intersection values, which I do not need. So, it may add an additional computational complexity which I do not need.

score 5 · Accepted Answer · answered Sep 30 '13 at 08:41

5

The java.util.Collections class provides useful methods for that:

boolean hasDuplicateValue(HashSet hs1, HashSet hs2) {        
  return !Collections.disjoint(hs1,hs2);
}

answered Sep 30 '13 at 08:41

Simiil

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score 4 · Answer 2 · 2013-09-30T08:39:20.307

4

Im not sure but do you talking about something like this ?

boolean hasDuplicateValue(HashSet hs1, HashSet hs2) {
    // you can add some null pointer defence if necessary
    if (hs2.size() == 0) {
        return false;
    }
    for (Object obj : hs1) {
        if (hs2.contains(obj)) {
            return true;
        }
    }
    return false;
}

edited Sep 30 '13 at 08:39

answered Sep 30 '13 at 08:28

2

just a note, if hs2 size is zero then he can return false immediately – upog Sep 30 '13 at 08:32
better use generics: `HashSet>` – John Dvorak Sep 30 '13 at 08:34
1

@upog even better: always iterate over the smaller set – John Dvorak Sep 30 '13 at 08:36
@Jan Dvorak in that case, the contains method need to iterate over the larger collection. so i doubt in this case whether it will improve performance .... – upog Sep 30 '13 at 08:44
@upog do you know how hash sets work? Lookup is O(1) – John Dvorak Sep 30 '13 at 08:49

score 0 · Answer 3 · answered Sep 30 '13 at 08:29

0

Take a look at the guava-libraries that provide a Sets which contains the intersect method. On the other side, this method takes two Set, not their implementation.

answered Sep 30 '13 at 08:29

Dimitri

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score 0 · Answer 4 · answered Sep 30 '13 at 08:34

0

To complete oleg.lukyrych answer: If you want to remove the warnings, on the declaration of the method: And it is a good practice to use Set instead of HashSet when possible :

<T> boolean hasDuplicateValue(Set<T> hs1, Set<T> hs2) {
    for (T obj : hs1) {
        if (hs2.contains(obj)) {
            return true;
        }
    }
    return false;
}

answered Sep 30 '13 at 08:34

fluminis

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Good advice. I just took the method signature from question body. Thought it would be most relevant :) – Sep 30 '13 at 08:40

Find out whether two HashSets have a duplicate value

4 Answers4