137 lines
7.2 KiB
Markdown
137 lines
7.2 KiB
Markdown
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---
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title: Dna Pairing
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---
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 Remember to use <a>**`Read-Search-Ask`**</a> if you get stuck. Try to pair program  and write your own code 
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###  Problem Explanation:
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* You will get a DNA strand sequence and you need to get the pair and return it as a 2D array of the base pairs. Keep in mind that the provided strand should be first always.
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* Another way to interpret the problem: there are four potential characters that exist in DNA: "A", "T", "G", and "C". "A" and "T" are always paired together, and "G" and "C" are always paired together.
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This problem presents you with an input, e.g. "ATCGA". Each of those five characters are missing their pairs.
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E.g. the first character "A" needs to be paired with "T" to give the array element ["A", "T"].
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The second character "T" needs to be paired with "A" to give the array element ["T", "A"].
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The number of elements in the final output equals the number of characters in the input.
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This problem does not involve rearranging the input into different combinations or permutations.
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#### Relevant Links
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* <a href='http://forum.freecodecamp.com/t/javascript-array-prototype-push/14298' target='_blank' rel='nofollow'>Array.push()</a>
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* <a href='http://forum.freecodecamp.com/t/javascript-string-prototype-split/15944' target='_blank' rel='nofollow'>String.split()</a>
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##  Hint: 1
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* There are two base case, A-T and C-G, these go both way. You can use regular expression, if statements of anything that you can think of.
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> _try to solve the problem now_
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##  Hint: 2
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* I would recommend using a switch, as it makes things a lot smoother.
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> _try to solve the problem now_
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##  Hint: 3
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* The result must be an array of arrays, so keep that in mind when pushing things.
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> _try to solve the problem now_
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## Spoiler Alert!
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**Solution ahead!**
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##  Basic Code Solution:
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```javascript
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function pairElement(str) {
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// Return each strand as an array of two elements, the original and the pair.
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var paired = [];
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// Function to check with strand to pair.
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var search = function(char) {
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switch (char) {
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case 'A':
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paired.push(['A', 'T']);
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break;
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case 'T':
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paired.push(['T', 'A']);
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break;
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case 'C':
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paired.push(['C', 'G']);
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break;
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case 'G':
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paired.push(['G', 'C']);
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break;
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}
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};
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// Loops through the input and pair.
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for (var i = 0; i < str.length; i++) {
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search(str[i]);
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}
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return paired;
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}
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// test here
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pairElement("GCG");
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```
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 <a href='https://repl.it/CLmz/0' target='_blank' rel='nofollow'>Run Code</a>
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### Code Explanation:
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* The program is very simple, the best solution that I have come up with is to use a switch to catch all the possible four elements. Using if statements would take too much code. You could also use Regular Expressions.
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* Since we have to the original and the pair, I decided to take all four cases instead of the base two.
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* Create an empty array and use the `search` function to push the right values to the array and return them.
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#### Relevant Links
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/switch' target='_blank' rel='nofollow'>Switch Statements</a>
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##  Intermediate Code Solution:
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```javascript
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function pairElement(str) {
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//create object for pair lookup
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var pairs = {
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"A": "T",
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"T": "A",
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"C": "G",
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"G": "C"
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}
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//split string into array of characters
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var arr = str.split("");
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//map character to array of character and matching pair
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return arr.map(x => [x,pairs[x]]);
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}
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//test here
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pairElement("GCG");
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```
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 <a href='https://repl.it/repls/ThoroughSphericalComputeranimation' target='_blank' rel='nofollow'>Run Code</a>
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## Code Explanation:
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* First define an object with all pair possibilities, this allows us to easily find by key or value.
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* Split `str` into a characters array so we can use each letter to find its pair.
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* Use the map function to map each character in the array to an array with the character and it's matching pair, creating a 2D array.
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#### Relevant Links
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map' target='_blank' rel='nofollow'>Array.prototype.map()</a>
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors' target='_blank' rel='nofollow'>Property accessors</a>
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* <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions' target='_blank' rel='nofollow'>Arrow functions</a>
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##  NOTES FOR CONTRIBUTIONS:
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*  **DO NOT** add solutions that are similar to any existing solutions. If you think it is **_similar but better_**, then try to merge (or replace) the existing similar solution.
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* Add an explanation of your solution.
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* Categorize the solution in one of the following categories — **Basic**, **Intermediate** and **Advanced**. 
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* Please add your username only if you have added any **relevant main contents**. ( **_DO NOT_** _remove any existing usernames_)
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> See  <a href='http://forum.freecodecamp.com/t/algorithm-article-template/14272' target='_blank' rel='nofollow'>**`Wiki Challenge Solution Template`**</a> for reference.
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