如何检查一对已经存在？

Question

I have a string say "abab" and im splitting it in pairs.(ie ab,ab) If pair already exists then i dont want it to be generated.How do i do it Here's the code for what ive tried

      String r="abab";
      String  pair[] = new String[r.length()/2];
      for( int i = 0; i <pair.length; i++ ) 
      {
          pair[i] = r.substring(i*2,(i*2)+2);
      }

Answer 1

Before adding it to the pair array you could see if it already exists with the Arrays function .contains. If the pair already exists then don't add it to the pair list. For example here the ab and fe pairs will not be added:

  String r="ababtefedefe";
  String  pair[] = new String[r.length()/2];
  String currentPair = "";
  for( int i = 0; i <pair.length; i++ ) 
  {
      currentPair = r.substring(i*2,(i*2)+2);
      if(!java.util.Arrays.asList(pair).contains(currentPair))
        pair[i] = currentPair;
      System.out.println(pair[i]);
  }

Answer 2

I would use a Set to help me out.

private String[] retrieveUniquePair(String input) {
    int dim = input.length() / 2;
    Set<String> pairs = new LinkedHashSet<>(dim);

    for (int i = 0; i <= dim; i += 2) {
        String currentPair = input.substring(i, i + 2);
        pairs.add(currentPair);
    }

    return pairs.toArray(new String[] {});
}

Edit: I post the solution I propose and the test

public class PairTest {

    @DataProvider(name = "input")
    public static Object[][] input() {
        return new Object[][] {
                {"abcd", Arrays.asList("ab", "cd")},
                {"abcde", Arrays.asList("ab", "cd")},
                {"abcdab", Arrays.asList("ab", "cd")},
                {"ababcdcd", Arrays.asList("ab", "cd")},
                {"ababtefedefe", Arrays.asList("ab", "te", "fe", "de")},
        };
    }

    @Test(dataProvider = "input")
    public void test(String input, List<String> expectedOutput) {
        String[] output = retrieveUniquePair(input);

        Assert.assertNotNull(output);
        Assert.assertEquals(output.length, expectedOutput.size());
        for (String pair : output) {
            Assert.assertTrue(expectedOutput.contains(pair));
        }
    }

    private String[] retrieveUniquePair(String input) {
        int pairNumber = input.length() / 2;
        Set<String> pairs = new LinkedHashSet<>(pairNumber);

        int endIteration = input.length();
        if (input.length() % 2 != 0) { // odd number
            endIteration--; // ignore last character
        }

        for (int i = 0; i < endIteration; i += 2) {
            String currentPair = input.substring(i, i + 2);
            pairs.add(currentPair);
        }

        return pairs.toArray(new String[pairs.size() - 1]);
    }
}