index.js

'use strict';

/**
 * Function `generateSentences` takes 2D array of words as input
 * Returns array of all the sentences possible to form using the words
 * It keeps the order of words same in sentence as given in input
 * First row will be first word in the sentence, second row will be second and so on
 * It will generate sentences equals to the number of rows in the 2D array
 */
const generateSentences = (wordsList) => {
  if (wordsList === null || wordsList.length === 0) {
    return null;
  }

  // To hold the temporary data
  const sentences = Array(wordsList.length).fill('');

  // Array to hold all the sentences formed.
  const generatedSentences = [];

  for (let i = 0; i < wordsList[0].length; i++) {
    generateSentencePermutations(wordsList, 0, i, sentences, generatedSentences);
  }

  return generatedSentences;
};

const generateSentencePermutations = (wordsList, startIndex, wordIndex, sentences, generateSentences) => {

  sentences[startIndex] = wordsList[startIndex][wordIndex];

  if (startIndex === (wordsList.length - 1)) {
    generateSentences.push(sentences.join(' '));
    return;
  }

  for (let i = 0; i < wordsList[startIndex + 1].length; i++) {
    generateSentencePermutations(wordsList, startIndex + 1, i, sentences, generateSentences);
  }
};

module.exports = generateSentences;