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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/symmetric-difference.md

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+---
+id: 5a23c84252665b21eecc8046
+title: Symmetric difference
+challengeType: 5
+forumTopicId: 16086
+---
+
+## Description
+
+<section id='description'>
+
+Given two <a href="https://rosettacode.org/wiki/set" target="_blank">set</a>s <i>A</i> and <i>B</i>, compute $(A \setminus B) \cup (B \setminus A).$
+That is, enumerate the items that are in <i>A</i> or <i>B</i> but not both. This set is called the <a href="https://en.wikipedia.org/wiki/Symmetric difference" target="_blank">symmetric difference</a> of <i>A</i> and <i>B</i>.
+In other words: $(A \cup B) \setminus (A \cap B)$ (the set of items that are in at least one of <i>A</i> or <i>B</i> minus the set of items that are in both <i>A</i> and <i>B</i>).
+
+</section>
+
+## Instructions
+
+<section id='instructions'>
+
+Write a function that takes two arrays as parameters and returns the symmetric difference. Sort the resultant array before returning it.
+
+</section>
+
+## Tests
+
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>symmetricDifference</code> should be a function.
+    testString: assert(typeof symmetricDifference == 'function');
+  - text: <code>symmetricDifference(["John", "Bob", "Mary", "Serena"], ["Jim", "Mary", "John", "Bob"])</code> should return an array.
+    testString: assert(Array.isArray(symmetricDifference(["John", "Bob", "Mary", "Serena"], ["Jim", "Mary", "John", "Bob"])));
+  - text: <code>symmetricDifference(["John", "Bob", "Mary", "Serena"], ["Jim", "Mary", "John", "Bob"])</code> should return <code>["Jim", "Serena"]</code>.
+    testString: assert.deepEqual(symmetricDifference(["John", "Bob", "Mary", "Serena"], ["Jim", "Mary", "John", "Bob"]), ["Jim", "Serena"]);
+  - text: <code>symmetricDifference([1, 2, 3], [3, 4])</code> should return <code>[1, 2, 4]</code>.
+    testString: assert.deepEqual(symmetricDifference([1, 2, 3], [3, 4]), [1, 2, 4]);
+  - text: <code>symmetricDifference([1, 2, 3, 4, 5], [3, 4, 8, 7])</code> should return <code>[1, 2, 5, 7, 8]</code>.
+    testString: assert.deepEqual(symmetricDifference([1, 2, 3, 4, 5], [3, 4, 8, 7]), [1, 2, 5, 7, 8]);
+  - text: <code>symmetricDifference([1, 2, 3, 4, 5, 6, 7, 8], [1, 3, 5, 6, 7, 8, 9])</code> should return <code>[2, 4, 9]</code>.
+    testString: assert.deepEqual(symmetricDifference([1, 2, 3, 4, 5, 6, 7, 8], [1, 3, 5, 6, 7, 8, 9]), [2, 4, 9]);
+  - text: <code>symmetricDifference([1, 2, 4, 7, 9], [2, 3, 7, 8, 9])</code> should return <code>[1, 3, 4, 8]</code>.
+    testString: assert.deepEqual(symmetricDifference([1, 2, 4, 7, 9], [2, 3, 7, 8, 9]), [1, 3, 4, 8]);
+```
+
+</section>
+
+## Challenge Seed
+
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function symmetricDifference(A, B) {
+
+}
+```
+
+</div>
+</section>
+
+## Solution
+
+<section id='solution'>
+
+```js
+function symmetricDifference(A, B) {
+  function relative_complement(A, B) {
+    return A.filter(function(elem) {
+      return B.indexOf(elem) == -1;
+    });
+  }
+
+  function unique(ary) {
+    var u = ary.concat().sort();
+    for (var i = 1; i < u.length; ) {
+      if (u[i - 1] === u[i]) u.splice(i, 1);
+      else i++;
+    }
+    return u;
+  }
+
+  return unique(
+    relative_complement(A, B).concat(relative_complement(B, A))
+  ).sort();
+}
+```
+
+</section>