Mark caesar as archived and move archived exercise to own folder (#336)

archive/archived_caesar/README.md

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+# Exercise 13 - Caesar cipher
+
+Implement the legendary Caesar cipher:
+
+> In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would become B, and so on. The method is named after Julius Caesar, who used it in his private correspondence.
+
+Hint: You may need to convert letters to their unicode values. Be sure to read the documentation!
+
+write a function that takes a string to be encoded and a shift factor and then returns the encoded string:
+
+```javascript
+caesar('A', 1) // simply shifts the letter by 1: returns 'B'
+```
+
+the cipher should retain capitalization:
+```javascript
+caesar('Hey', 5) // returns 'Mjd'
+```
+
+should _not_ shift punctuation:
+```javascript
+caesar('Hello, World!', 5) //returns 'Mjqqt, Btwqi!'
+```
+
+the shift should wrap around the alphabet:
+```javascript
+caesar('Z', 1) // returns 'A'
+```
+
+negative numbers should work as well:
+```javascript
+caesar('Mjqqt, Btwqi!', -5) // returns 'Hello, World!'
+```

archive/archived_caesar/caesar.js

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+const caesar = function() {
+
+};
+
+// Do not edit below this line
+module.exports = caesar;

archive/archived_caesar/caesar.spec.js

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+const caesar = require('./caesar')
+
+test('works with single letters', () => {
+  expect(caesar('A', 1)).toBe('B');
+});
+test.skip('works with words', () => {
+  expect(caesar('Aaa', 1)).toBe('Bbb');
+});
+test.skip('works with phrases', () => {
+  expect(caesar('Hello, World!', 5)).toBe('Mjqqt, Btwqi!');
+});
+test.skip('works with negative shift', () => {
+  expect(caesar('Mjqqt, Btwqi!', -5)).toBe('Hello, World!');
+});
+test.skip('wraps', () => {
+  expect(caesar('Z', 1)).toBe('A');
+});
+test.skip('works with large shift factors', () => {
+  expect(caesar('Hello, World!', 75)).toBe('Ebiil, Tloia!');
+});
+test.skip('works with large negative shift factors', () => {
+  expect(caesar('Hello, World!', -29)).toBe('Ebiil, Tloia!');
+});

archive/archived_caesar/solution/caesar-solution.js

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+const caesar = function (string, shift) {
+  return string
+    .split("")
+    .map((char) => shiftChar(char, shift))
+    .join("");
+};
+
+const codeSet = (code) => (code < 97 ? 65 : 97);
+
+// this function is just a fancy way of doing % so that it works with negative numbers
+// see this link for details:
+// https://stackoverflow.com/questions/4467539/javascript-modulo-gives-a-negative-result-for-negative-numbers
+const mod = (n, m) => ((n % m) + m) % m;
+
+const shiftChar = (char, shift) => {
+  const code = char.charCodeAt();
+
+  if ((code >= 65 && code <= 90) || (code >= 97 && code <= 122)) {
+    return String.fromCharCode(
+      mod(code + shift - codeSet(code), 26) + codeSet(code)
+    );
+  }
+  return char;
+};
+
+module.exports = caesar;

archive/archived_caesar/solution/caesar-solution.spec.js

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+const caesar = require('./caesar-solution');
+
+test('works with single letters', () => {
+  expect(caesar('A', 1)).toBe('B');
+});
+test('works with words', () => {
+  expect(caesar('Aaa', 1)).toBe('Bbb');
+});
+test('works with phrases', () => {
+  expect(caesar('Hello, World!', 5)).toBe('Mjqqt, Btwqi!');
+});
+test('works with negative shift', () => {
+  expect(caesar('Mjqqt, Btwqi!', -5)).toBe('Hello, World!');
+});
+test('wraps', () => {
+  expect(caesar('Z', 1)).toBe('A');
+});
+test('works with large shift factors', () => {
+  expect(caesar('Hello, World!', 75)).toBe('Ebiil, Tloia!');
+});
+test('works with large negative shift factors', () => {
+  expect(caesar('Hello, World!', -29)).toBe('Ebiil, Tloia!');
+});