127 lines
5.9 KiB
Markdown
127 lines
5.9 KiB
Markdown
---
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id: 5a23c84252665b21eecc8029
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title: Straddling checkerboard
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challengeType: 5
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isHidden: false
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forumTopicId: 302325
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---
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## Description
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<section id='description'>
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Implement functions to encrypt and decrypt a message using the <a href="https://en.wikipedia.org/wiki/Straddling_checkerboard">straddling checkerboard</a> method. The functions will take a string and an array as parameters. The array has 3 strings representing the 3 rows of the checkerboard. The output will be a series of decimal digits.
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Numbers should be encrypted by inserting the escape character before each digit, then including the digit unencrypted. This should be reversed for decryption.
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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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tests:
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- text: <code>straddle</code> should be a function.
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testString: assert(typeof straddle == 'function');
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- text: <code>straddle("One night-it was on the twentieth of March, 1888-I was returning.",["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"])</code> should return a string.
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testString: assert(typeof straddle("One night-it was on the twentieth of March, 1888-I was returning.", ["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"]) == 'string');
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- text: <code>straddle("One night-it was on the twentieth of March, 1888-I was returning.",["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"])</code> should return <code>"34045747525284613427502840425027537379697175891898898898584619028294547488"</code>.
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testString: assert.equal(straddle("One night-it was on the twentieth of March, 1888-I was returning.", ["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"]), "34045747525284613427502840425027537379697175891898898898584619028294547488");
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- text: <code>straddle("One night-it was on the twentieth of March, 1888-I was returning",["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"])</code> should return <code>"139539363509369743061399059745399365901344308320791798798798367430685972839363935"</code>.
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testString: assert.equal(straddle("One night-it was on the twentieth of March, 1888-I was returning", ["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"]), "139539363509369743061399059745399365901344308320791798798798367430685972839363935");
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- text: <code>straddle("Thecheckerboardcakerecipespecifies3largeeggsand2.25cupsofflour.",["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."])</code> should return <code>"125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769"</code>.
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testString: assert.equal(straddle("Thecheckerboardcakerecipespecifies3largeeggsand2.25cupsofflour.", ["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."]), "125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769");
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- text: <code>unstraddle</code> should be a function.
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testString: assert(typeof unstraddle == 'function');
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- text: <code>unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488",["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"])</code> should return a string.
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testString: assert(typeof unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488", ["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"]) == 'string');
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- text: <code>unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488",["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"])</code> should return <code>"ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING."</code>.
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testString: assert.equal(unstraddle("34045747525284613427502840425027537379697175891898898898584619028294547488", ["ESTONIA R", "BCDFGHJKLM", "PQUVWXYZ./"]), "ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING.");
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- text: <code>unstraddle("139539363509369743061399059745399365901344308320791798798798367430685972839363935",["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"])</code> should return <code>"ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING"</code>.
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testString: assert.equal(unstraddle("139539363509369743061399059745399365901344308320791798798798367430685972839363935", ["HOL MES RT", "ABCDFGIJKN", "PQUVWXYZ./"]), "ONENIGHTITWASONTHETWENTIETHOFMARCH1888IWASRETURNING");
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- text: <code>unstraddle("125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769",["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."])</code> should return <code>"THECHECKERBOARDCAKERECIPESPECIFIES3LARGEEGGSAND2.25CUPSOFFLOUR."</code>.
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testString: assert.equal(unstraddle("125021250212707204372221327070218600960021823809623283724002424935226226962262521636094232328463769", ["ET AON RIS", "BCDFGHJKLM", "PQ/UVWXYZ."]), "THECHECKERBOARDCAKERECIPESPECIFIES3LARGEEGGSAND2.25CUPSOFFLOUR.");
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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 straddle(message, alphabet) {
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// Good luck!
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}
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function unstraddle(message, alphabet) {
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// Good luck!
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}
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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 straddle(message, alphabet) {
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var prefixes = new Array(
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'',
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alphabet[0].indexOf(' '),
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alphabet[0].lastIndexOf(' ')
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);
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var out = '';
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message = message.toUpperCase();
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message = message.replace(/([0-9])/g, '/$1'); // dumb way to escape numbers
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for (var i = 0; i < message.length; i++) {
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var chr = message[i];
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if (chr == ' ') continue;
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for (var j = 0; j < 3; j++) {
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var k = alphabet[j].indexOf(chr);
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if (k < 0) continue;
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out += prefixes[j].toString() + k;
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}
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if (chr == '/') out += message[++i];
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}
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return out;
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}
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function unstraddle(message, alphabet) {
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var prefixes = new Array(
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'',
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alphabet[0].indexOf(' '),
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alphabet[0].lastIndexOf(' ')
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);
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var out = '';
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var n, o;
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for (var i = 0; i < message.length; i++) {
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n = message[i] * 1;
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switch (n) {
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case prefixes[1]:
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o = alphabet[1][message[++i]];
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break;
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case prefixes[2]:
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o = alphabet[2][message[++i]];
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break;
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default:
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o = alphabet[0][n];
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}
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o == '/' ? (out += message[++i]) : (out += o);
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}
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return out;
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}
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```
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</section>
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