freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/algorithms/find-the-symmetric-difference.english.md

id	title	challengeType
a3f503de51cf954ede28891d	Find the Symmetric Difference	5

Description

Create a function that takes two or more arrays and returns an array of the symmetric difference (△ or ⊕) of the provided arrays. Given two sets (for example set A = {1, 2, 3} and set B = {2, 3, 4}), the mathematical term "symmetric difference" of two sets is the set of elements which are in either of the two sets, but not in both (A △ B = C = {1, 4}). For every additional symmetric difference you take (say on a set D = {2, 3}), you should get the set with elements which are in either of the two the sets but not both (C △ D = {1, 4} △ {2, 3} = {1, 2, 3, 4}). The resulting array must contain only unique values (no duplicates). Remember to use Read-Search-Ask if you get stuck. Try to pair program. Write your own code.

Instructions

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], '<code>sym([1, 2, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.');
  - 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, '<code>sym([1, 2, 3], [5, 2, 1, 4])</code> should contain only three elements.');
  - 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], '<code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.');
  - 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, '<code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should contain only three elements.');
  - 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], '<code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should return <code>[3, 4, 5]</code>.');
  - 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, '<code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should contain only three elements.');
  - 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], '<code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should return <code>[1, 4, 5]</code>');
  - 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, '<code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should contain only three elements.');
  - 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], '<code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should return <code>[1, 4, 5]</code>.');
  - 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, '<code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should contain only three elements.');
  - 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], '<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>.');
  - 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, '<code>sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3])</code> should contain only five elements.');
  - 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], '<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>.');
  - 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, '<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.');

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]);