74 lines
2.4 KiB
Markdown
74 lines
2.4 KiB
Markdown
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---
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id: afd15382cdfb22c9efe8b7de
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title: DNA Pairing
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isRequired: true
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challengeType: 5
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---
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## Description
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<section id='description'>
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The DNA strand is missing the pairing element. Take each character, get its pair, and return the results as a 2d array.
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<a href="http://en.wikipedia.org/wiki/Base_pair" target="_blank">Base pairs</a> are a pair of AT and CG. Match the missing element to the provided character.
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Return the provided character as the first element in each array.
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For example, for the input GCG, return [["G", "C"], ["C","G"],["G", "C"]]
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The character and its pair are paired up in an array, and all the arrays are grouped into one encapsulating array.
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Remember to use <a href='http://forum.freecodecamp.org/t/how-to-get-help-when-you-are-stuck/19514' target='_blank'>Read-Search-Ask</a> if you get stuck. Try to pair program. Write your own code.
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</section>
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## Instructions
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<section id='instructions'>
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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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- text: '<code>pairElement("ATCGA")</code> should return <code>[["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]</code>.'
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testString: 'assert.deepEqual(pairElement("ATCGA"),[["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]], "<code>pairElement("ATCGA")</code> should return <code>[["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]</code>.");'
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- text: '<code>pairElement("TTGAG")</code> should return <code>[["T","A"],["T","A"],["G","C"],["A","T"],["G","C"]]</code>.'
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testString: 'assert.deepEqual(pairElement("TTGAG"),[["T","A"],["T","A"],["G","C"],["A","T"],["G","C"]], "<code>pairElement("TTGAG")</code> should return <code>[["T","A"],["T","A"],["G","C"],["A","T"],["G","C"]]</code>.");'
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- text: '<code>pairElement("CTCTA")</code> should return <code>[["C","G"],["T","A"],["C","G"],["T","A"],["A","T"]]</code>.'
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testString: 'assert.deepEqual(pairElement("CTCTA"),[["C","G"],["T","A"],["C","G"],["T","A"],["A","T"]], "<code>pairElement("CTCTA")</code> should return <code>[["C","G"],["T","A"],["C","G"],["T","A"],["A","T"]]</code>.");'
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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 pairElement(str) {
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return str;
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}
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pairElement("GCG");
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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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var lookup = Object.create(null);
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lookup.A = 'T';
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lookup.T = 'A';
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lookup.C = 'G';
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lookup.G = 'C';
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function pairElement(str) {
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return str.split(").map(function(p) {return [p, lookup[p]];});
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}
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```
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</section>
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