93 lines
3.2 KiB
Markdown
93 lines
3.2 KiB
Markdown
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---
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id: 56533eb9ac21ba0edf2244e2
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title: Caesars Cipher
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challengeType: 5
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isRequired: true
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---
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## Description
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<section id='description'>
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One of the simplest and most widely known <dfn>ciphers</dfn> is a <code>Caesar cipher</code>, also known as a <code>shift cipher</code>. In a <code>shift cipher</code> the meanings of the letters are shifted by some set amount.
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A common modern use is the <a href="https://en.wikipedia.org/wiki/ROT13" target='_blank'>ROT13</a> cipher, where the values of the letters are shifted by 13 places. Thus 'A' ↔ 'N', 'B' ↔ 'O' and so on.
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Write a function which takes a <a href="https://en.wikipedia.org/wiki/ROT13" target='_blank'>ROT13</a> encoded string as input and returns a decoded string.
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All letters will be uppercase. Do not transform any non-alphabetic character (i.e. spaces, punctuation), but do pass them on.
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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>rot13("SERR PBQR PNZC")</code> should decode to <code>FREE CODE CAMP</code>
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testString: 'assert(rot13("SERR PBQR PNZC") === "FREE CODE CAMP", "<code>rot13("SERR PBQR PNZC")</code> should decode to <code>FREE CODE CAMP</code>");'
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- text: <code>rot13("SERR CVMMN!")</code> should decode to <code>FREE PIZZA!</code>
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testString: 'assert(rot13("SERR CVMMN!") === "FREE PIZZA!", "<code>rot13("SERR CVMMN!")</code> should decode to <code>FREE PIZZA!</code>");'
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- text: <code>rot13("SERR YBIR?")</code> should decode to <code>FREE LOVE?</code>
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testString: 'assert(rot13("SERR YBIR?") === "FREE LOVE?", "<code>rot13("SERR YBIR?")</code> should decode to <code>FREE LOVE?</code>");'
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- text: <code>rot13("GUR DHVPX OEBJA SBK WHZCF BIRE GUR YNML QBT.")</code> should decode to <code>THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.</code>
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testString: 'assert(rot13("GUR DHVPX OEBJA SBK WHZCF BIRE GUR YNML QBT.") === "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.", "<code>rot13("GUR DHVPX OEBJA SBK WHZCF BIRE GUR YNML QBT.")</code> should decode to <code>THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.</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 rot13(str) { // LBH QVQ VG!
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return str;
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}
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// Change the inputs below to test
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rot13("SERR PBQR PNZC");
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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 = {
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'A': 'N','B': 'O','C': 'P','D': 'Q',
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'E': 'R','F': 'S','G': 'T','H': 'U',
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'I': 'V','J': 'W','K': 'X','L': 'Y',
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'M': 'Z','N': 'A','O': 'B','P': 'C',
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'Q': 'D','R': 'E','S': 'F','T': 'G',
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'U': 'H','V': 'I','W': 'J','X': 'K',
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'Y': 'L','Z': 'M'
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};
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function rot13(encodedStr) {
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var codeArr = encodedStr.split(""); // String to Array
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var decodedArr = []; // Your Result goes here
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// Only change code below this line
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decodedArr = codeArr.map(function(letter) {
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if(lookup.hasOwnProperty(letter)) {
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letter = lookup[letter];
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}
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return letter;
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});
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// Only change code above this line
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return decodedArr.join(""); // Array to String
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}
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```
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</section>
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