finding patterns in an array

algorithm, java

Solution

UPDATE: I implemented the approach I was describing.

Running the code below returns:

First match against pattern found at index 3
No match found.

I put the code and the test code inside one class for the sake of simplicity. The function that does the work is findPatternIndex. The rest is simple test, init, and display logic.

import java.util.LinkedHashMap;
import java.util.Map;

import org.junit.Before;
import org.junit.Test;

public class PatternMatching {

  private final Map<String, Character> encodedWords = new LinkedHashMap<String, Character>();

  @Before
  public void init() {
    encodedWords.put("Angry", 'A');
    encodedWords.put("Smile", 'S');
    encodedWords.put("Frown", 'F');
  }

  public int findPatternIndex(final String[] array, final String pattern) {
    final StringBuffer encodedSequence = new StringBuffer();
    for (final String element : array) {
      encodedSequence.append(encodedWords.get(element));
    }
    return encodedSequence.toString().indexOf(pattern);
  }

  private void displayFindings(final int index) {
    if (index==-1) {
      System.out.println("No match found.");
    } else {
      System.out.println("First match against pattern found at index " + index);
    }
  }

  @Test
  public void shouldFindOneMatchThenNone() {
    final String[] array = {"Angry","Angry","Angry","Smile","Frown","Smile","Frown","Smile","Frown","Angry","Frown","Angry","Frown","Smile"};
    String pattern="SFSF";
    displayFindings(findPatternIndex(array, pattern));
    pattern="AAF";
    displayFindings(findPatternIndex(array, pattern));
  }

}

The code could further be updated to build encodedWords dynamically if the words populating the array are not known in advance. It would also be simple enough to display the index of all matches instead of just the first one.

Problem

Original source