Find all combinations in dictionary

findCombinationsFromDictionary.js

function reduceWord(active, rest, subsequences) {
  if (!active && !rest) {
    return;          
  }

  if (!rest) {
    subsequences.push(active);
  } else {
    reduceWord(active + rest[0], rest.slice(1), subsequences);
    reduceWord(active, rest.slice(1), subsequences);
  }

  return subsequences;
} 

function getSubWords(word) {
  return reduceWord("", word, []);
}

function findAnagrams(dictionary, word){
    const anagrams = [];
    const alphabetizeWord = alphabetize(word);
  
    dictionary.forEach((entry) => {
        if (alphabetizeWord === alphabetize(entry)) {
            anagrams.push(entry);
        }
     });
  
    return anagrams;
}

function alphabetize(word) { 
    return word && word.split('').sort().join('');
}

function findCombinationsFromDictionary(dictionary, word) {
  const combinations = getSubWords(word);
  const results = [];
  
  combinations.forEach((permutation) => {
    const anagrams = findAnagrams(dictionary, permutation);
    results.push(anagrams);
  });
  
  return results.flat();
}

mocha.setup('bdd');
const assert = chai.assert;

describe('findCombinationsFromDictionary', () => {
  
  it('finds all combinations of a word in a given dictionary', () => {
    const dictionary = ['act', 'tar', 'far', 'cat', 'tac', 'sat', 'hat', 'dog', 'at'];
    const anagrams = findCombinationsFromDictionary(dictionary, 'cat');
    assert.deepEqual(anagrams, ["act", "cat", "tac", "at"]);
  }); 
  
  it('returns an empty array if there are no combinations in a given dictionary', () => {
    const dictionary = ['act', 'tar', 'far', 'cat', 'tac', 'sat', 'hat', 'dog', 'at'];
    const anagrams = findCombinationsFromDictionary(dictionary, 'foo');
    
    assert.deepEqual(anagrams, []);
  }); 
  
});

mocha.run();