96 lines
4.4 KiB
Markdown
96 lines
4.4 KiB
Markdown
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---
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id: a3f503de51cf954ede28891d
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title: Find the Symmetric Difference
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challengeType: 5
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forumTopicId: 301611
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---
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## Description
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<section id='description'>
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The mathematical term <dfn>symmetric difference</dfn> (<code>△</code> or <code>⊕</code>) of two sets is the set of elements which are in either of the two sets but not in both. For example, for sets <code>A = {1, 2, 3}</code> and <code>B = {2, 3, 4}</code>, <code>A △ B = {1, 4}</code>.
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Symmetric difference is a binary operation, which means it operates on only two elements. So to evaluate an expression involving symmetric differences among <em>three</em> elements (<code>A △ B △ C</code>), you must complete one operation at a time. Thus, for sets <code>A</code> and <code>B</code> above, and <code>C = {2, 3}</code>, <code>A △ B △ C = (A △ B) △ C = {1, 4} △ {2, 3} = {1, 2, 3, 4}</code>.
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</section>
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## Instructions
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<section id='instructions'>
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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 (<em>no duplicates</em>).
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>sym([1, 2, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.
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testString: assert.sameMembers(sym([1, 2, 3], [5, 2, 1, 4]), [3, 4, 5]);
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- text: <code>sym([1, 2, 3], [5, 2, 1, 4])</code> should contain only three elements.
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testString: assert.equal(sym([1, 2, 3], [5, 2, 1, 4]).length, 3);
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- text: <code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should return <code>[3, 4, 5]</code>.
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testString: assert.sameMembers(sym([1, 2, 3, 3], [5, 2, 1, 4]), [3, 4, 5]);
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- text: <code>sym([1, 2, 3, 3], [5, 2, 1, 4])</code> should contain only three elements.
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testString: assert.equal(sym([1, 2, 3, 3], [5, 2, 1, 4]).length, 3);
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- text: <code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should return <code>[3, 4, 5]</code>.
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testString: assert.sameMembers(sym([1, 2, 3], [5, 2, 1, 4, 5]), [3, 4, 5]);
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- text: <code>sym([1, 2, 3], [5, 2, 1, 4, 5])</code> should contain only three elements.
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testString: assert.equal(sym([1, 2, 3], [5, 2, 1, 4, 5]).length, 3);
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- text: <code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should return <code>[1, 4, 5]</code>
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testString: assert.sameMembers(sym([1, 2, 5], [2, 3, 5], [3, 4, 5]), [1, 4, 5]);
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- text: <code>sym([1, 2, 5], [2, 3, 5], [3, 4, 5])</code> should contain only three elements.
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testString: assert.equal(sym([1, 2, 5], [2, 3, 5], [3, 4, 5]).length, 3);
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- text: <code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should return <code>[1, 4, 5]</code>.
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testString: assert.sameMembers(sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]), [1, 4, 5]);
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- text: <code>sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5])</code> should contain only three elements.
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testString: assert.equal(sym([1, 1, 2, 5], [2, 2, 3, 5], [3, 4, 5, 5]).length, 3);
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- 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>.
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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]);
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- 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.
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testString: assert.equal(sym([3, 3, 3, 2, 5], [2, 1, 5, 7], [3, 4, 6, 6], [1, 2, 3]).length, 5);
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- 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>.
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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]);
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- 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.
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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);
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function sym(args) {
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return args;
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}
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sym([1, 2, 3], [5, 2, 1, 4]);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function sym() {
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var arrays = [].slice.call(arguments);
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return arrays.reduce(function (symDiff, arr) {
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return symDiff.concat(arr).filter(function (val, idx, theArr) {
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return theArr.indexOf(val) === idx
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&& (symDiff.indexOf(val) === -1 || arr.indexOf(val) === -1);
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});
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});
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}
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sym([1, 2, 3], [5, 2, 1, 4]);
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```
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</section>
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