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fix(curriculum): Clarify definition of "symmetric difference" (#38792)

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* Clarify definition of "symmetric difference"

* Add definition of binary operation

* Adjust wording in "Symmetric Difference"

* Improve preposition use

* Move instructions to the Instructions section

Co-authored-by: Eric Leung <eric@erictleung.com>
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Ty Mick 2020-05-20 05:28:16 -04:00 committed by GitHub
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curriculum/challenges/english/08-coding-interview-prep/algorithms/find-the-symmetric-difference.english.md
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@ -7,13 +7,14 @@ forumTopicId: 301611
## Description
<section id='description'>
Create a function that takes two or more arrays and returns an array of the <dfn>symmetric difference</dfn> (<code>&xutri;</code> or <code>&oplus;</code>) of the provided arrays.
Given two sets (for example set <code>A = {1, 2, 3}</code> and set <code>B = {2, 3, 4}</code>), 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 (<code>A &xutri; B = C = {1, 4}</code>). For every additional symmetric difference you take (say on a set <code>D = {2, 3}</code>), you should get the set with elements which are in either of the two the sets but not both (<code>C &xutri; D = {1, 4} &xutri; {2, 3} = {1, 2, 3, 4}</code>). The resulting array must contain only unique values (<em>no duplicates</em>).
The mathematical term <dfn>symmetric difference</dfn> (<code>&xutri;</code> or <code>&oplus;</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 &xutri; B = {1, 4}</code>.
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 &xutri; B &xutri; 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 &xutri; B &xutri; C = (A &xutri; B) &xutri; C = {1, 4} &xutri; {2, 3} = {1, 2, 3, 4}</code>.
</section>
## Instructions
<section id='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 (<em>no duplicates</em>).
</section>
## Tests