--update: replaced indexof with Map(), throw error on missing arguments

Author: ashokdey

src/_Classics_/caeser_cipher/index.js

@@ -5,6 +5,8 @@
  */
 
 function caesarCipher(str, num) {
+  if (!num) throw new Error('Missing argument: num');
+
   const lowerCaseString = str.toLowerCase();
   const alphabets = 'abcdefghijklmnopqrstuvwxyz'.split('');
   const totalAlphabets = alphabets.length;
@@ -13,6 +15,12 @@ function caesarCipher(str, num) {
   // handle large number, like 300 or -300
   num %= totalAlphabets;
 
+  const alphabetsMap = new Map();
+
+  for (const index in alphabets) {
+    alphabetsMap[alphabets[index]] = index;
+  }
+
   for (let index in lowerCaseString) {
     // get the current character
     const currentCharacter = lowerCaseString[index];
@@ -24,7 +32,13 @@ function caesarCipher(str, num) {
     }
 
     // determine the new index
-    const currentIndex = alphabets.indexOf(currentCharacter);
+    /**
+     * const currentIndex = alphabets.indexOf(currentCharacter);
+     *
+     * With indexOf complexity will be O(n*26)
+     * With Map complexity will be O(n).
+     */
+    const currentIndex = Number(alphabetsMap[currentCharacter]);
     let newIndex = currentIndex + num;
 
     // if the index passes 25, restart from 0