getPermutations.js

// Recursive Solution
function getPermutations(string) {
  let permutations = new Set();
  const helper = (word, letters) => {
    if (!letters) {
      permutations.add(word);
      return;
    }
    for (let i = 0; i < letters.length; i++) {
      helper(word + letters[i], letters.slice(0, i) + letters.slice(i + 1));
    }
    return;
  }
  helper('', string);
  return permutations;
}


















// Tests

let desc = 'empty string';
let input = '';
let actual = getPermutations(input);
let expected = new Set(['']);
assert(isSetsEqual(actual, expected), desc);

desc = 'one character string';
input = 'a';
actual = getPermutations(input);
expected = new Set(['a']);
assert(isSetsEqual(actual, expected), desc);

desc = 'two character string';
input = 'ab';
actual = getPermutations(input);
expected = new Set(['ab', 'ba']);
assert(isSetsEqual(actual, expected), desc);

desc = 'three character string';
input = 'abc';
actual = getPermutations(input);
expected = new Set(['abc', 'acb', 'bac', 'bca', 'cab', 'cba']);
assert(isSetsEqual(actual, expected), desc);

function isSetsEqual(as, bs) {
  if (as.size !== bs.size) {
    return false;
  }
  for (let a of as) {
    if (!bs.has(a)) return false;
  }
  return true;
}

function assert(condition, desc) {
  if (condition) {
    console.log(`${desc} ... PASS`);
  } else {
    console.log(`${desc} ... FAIL`);
  }
}