Rename to CaesarCipher (#1144)

Ciphers/CaesarCipher.js

@@ -0,0 +1,32 @@
+/**
+ * @function caesarsCipher
+ * @description - 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.
+ * @see - [wiki](https://en.wikipedia.org/wiki/Caesar_cipher)
+ * @param  {string} str - string to be encrypted
+ * @param {number} rotation - the number of rotation, expect real number ( > 0)
+ * @return {string} - decrypted string
+ */
+const caesarCipher = (str, rotation) => {
+  if (typeof str !== 'string' || !Number.isInteger(rotation) || rotation < 0) {
+    throw new TypeError('Arguments are invalid')
+  }
+
+  const alphabets = new Array(26)
+    .fill()
+    .map((_, index) => String.fromCharCode(97 + index)) // generate all lower alphabets array a-z
+
+  const cipherMap = alphabets.reduce(
+    (map, char, index) => map.set(char, alphabets[(rotation + index) % 26]),
+    new Map()
+  )
+
+  return str.replace(/[a-z]/gi, (char) => {
+    if (/[A-Z]/.test(char)) {
+      return cipherMap.get(char.toLowerCase()).toUpperCase()
+    }
+
+    return cipherMap.get(char)
+  })
+}
+
+export default caesarCipher