Best way to find duplicates from two List

Question

In Java, I have two ArrayLists:

A = [Ab, cd, df, FE, ...]
B = [ab, cde, de, fE, ...]

If the lists are a little big, the brute force method is very slow:

for(String a : A) {
  for(String b : B) {
     if(a.equalsIgnoreCase(b)) {
        System.out.println("duplicate: " + a "->" + b);
     }
  }
}

What's the best way to make it faster, but not super complicated to implement?

Sets and an appropriate comparison function. – Savior Apr 07 '16 at 17:53 — Savior, Apr 07 '16 at 17:53

score 2 · Answer 1 · answered Apr 07 '16 at 17:56

2

simplest implementation is to use sets, like following:

final String A[] = {"Ab", "cd", "df", "FE"};
final String B[] = {"ab", "cde", "de", "fE"};

final Set<String> set = new HashSet<>(A.length);
for (final String a : A)
    set.add(a.toLowerCase());
for (final String b : B)
    if (set.contains(b.toLowerCase()))
        System.out.println("duplicate: " + b);

answered Apr 07 '16 at 17:56

Iłya Bursov

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what about if the problem requires to remove duplicates from list A? – user697911 Apr 07 '16 at 18:31
@user697911 then use `List`, iterator and its `remove` method – Iłya Bursov Apr 07 '16 at 19:30

Best way to find duplicates from two List

1 Answers1