freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/algorithms/find-the-symmetric-difference.md

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
a3f503de51cf954ede28891d	Find the Symmetric Difference	5	301611

Description

The mathematical term symmetric difference (△ or ⊕) of two sets is the set of elements which are in either of the two sets but not in both. For example, for sets A = {1, 2, 3} and B = {2, 3, 4}, A △ B = {1, 4}.

Symmetric difference is a binary operation, which means it operates on only two elements. So to evaluate an expression involving symmetric differences among three elements (A △ B △ C), you must complete one operation at a time. Thus, for sets A and B above, and C = {2, 3}, A △ B △ C = (A △ B) △ C = {1, 4} △ {2, 3} = {1, 2, 3, 4}.

Instructions

Create a function that takes two or more arrays and returns an array of their symmetric difference. The returned array must contain only unique values (no duplicates).

Tests

tests:
  - text: <code>sym([1, 2, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.
    testString: assert.sameMembers(sym([1, 2, 3], [5, 2, 1, 4]), [3, 4, 5]);
  - text: <code>sym([1, 2, 3], [5, 2, 1, 4])</code> should contain only three elements.
    testString: assert.equal(sym([1, 2, 3], [5, 2, 1, 4]).length, 3);
  - text: <code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.
    testString: assert.sameMembers(sym([1, 2, 3, 3], [5, 2, 1, 4]), [3, 4, 5]);
  - text: <code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should contain only three elements.
    testString: assert.equal(sym([1, 2, 3, 3], [5, 2, 1, 4]).length, 3);
  - text: <code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should return <code>[3, 4, 5]</code>.
    testString: assert.sameMembers(sym([1, 2, 3], [5, 2, 1, 4, 5]), [3, 4, 5]);
  - text: <code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should contain only three elements.
    testString: assert.equal(sym([1, 2, 3], [5, 2, 1, 4, 5]).length, 3);
  - text: <code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should return <code>[1, 4, 5]</code>
    testString: assert.sameMembers(sym([1, 2, 5], [2, 3, 5], [3, 4, 5]), [1, 4, 5]);
  - text: <code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should contain only three elements.
    testString: assert.equal(sym([1, 2, 5], [2, 3, 5], [3, 4, 5]).length, 3);
  - text: <code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should return <code>[1, 4, 5]</code>.
    testString: assert.sameMembers(sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]), [1, 4, 5]);
  - text: <code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should contain only three elements.
    testString: assert.equal(sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]).length, 3);
  - text: <code>sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3])</code> should return <code>[2, 3, 4, 6, 7]</code>.
    testString: assert.sameMembers(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]), [2, 3, 4, 6, 7]);
  - text: <code>sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3])</code> should contain only five elements.
    testString: assert.equal(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]).length, 5);
  - text: <code>sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1])</code> should return <code>[1, 2, 4, 5, 6, 7, 8, 9]</code>.
    testString: assert.sameMembers(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1]), [1, 2, 4, 5, 6, 7, 8, 9]);
  - text: <code>sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1])</code> should contain only eight elements.
    testString: assert.equal(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3], [5, 3, 9, 8], [1]).length, 8);

Challenge Seed

function sym(args) {
  return args;
}

sym([1, 2, 3], [5, 2, 1, 4]);

Solution

function sym() {
  var arrays = [].slice.call(arguments);
  return arrays.reduce(function (symDiff, arr) {
    return symDiff.concat(arr).filter(function (val, idx, theArr) {
      return theArr.indexOf(val) === idx
        && (symDiff.indexOf(val) === -1 || arr.indexOf(val) === -1);
    });
  });
}
sym([1, 2, 3], [5, 2, 1, 4]);