JavaScript Katas: Position in Alphabet

2020-08-04

Intro 🌐

Problem solving is an important skill, for your career and your life in general.

That's why I take interesting katas of all levels, customize them and explain how to solve them.

Understanding the Exercise❗

First, we need to understand the exercise! If you don't understand it, you can't solve it!.

My personal method:

Input: What do I put in?
Output: What do I want to get out?

Today's exercise

Source: Codewars

Write a function positionInAlphabet, that accepts one parameter: myChar.

Given a one-char string, e.g. "a", return the message "Position in Alphabet: [position]", e.g. "Position in Alphabet: 1". If the input is uppercase, handle it like a lowercase character.

Input: a string.

Output: a string.

Thinking about the Solution 💭

I think I understand the exercise (= what I put into the function and what I want to get out of it).

Now, I need the specific steps to get from input to output.

I try to do this in small baby steps:

Convert the character into lowercase
Find the position of the char in the alphabet
Return the desired message with the position

Example:

Input: "a"
Convert the character into lowercase: "a"
Find the position of the char in the alphabet: 1
Return the desired message with the position: "Position in Alphabet: 1"
Output: "Position in Alphabet: 1" ✅

Implementation (charCodeAt) ⛑

function positionInAlphabet(myChar) {
  const DIFFERENCE_CHARCODE_AND_LETTERS = 96;

  // Convert the character into lowercase
  const myCharLowercase = myChar.toLowerCase();

  // Find the position of the char in the alphabet
  const position =
    myCharLowercase.charCodeAt() - DIFFERENCE_CHARCODE_AND_LETTERS;

  // Return the desired message with the position
  return `Position in Alphabet: ${position}`;
}

Where do we get the 96 from? When we go to the ASCII Table and scroll down to the a in the Char column, we can see 97 in the Number column. So our 1. char has the number 97, our 2. char has number 98 etc., meaning there is a difference of 96 between the char code (the Number column) and the actual char (the Char column).

Result

console.log(positionInAlphabet("a"));
// 1 ✅

console.log(positionInAlphabet("Z"));
// 26  ✅

Implementation (indexOf) ⛑

function positionInAlphabet(myChar) {
  const letters = [
    "a",
    "b",
    "c",
    "d",
    "e",
    "f",
    "g",
    "h",
    "i",
    "j",
    "k",
    "l",
    "m",
    "n",
    "o",
    "p",
    "q",
    "r",
    "s",
    "t",
    "u",
    "v",
    "w",
    "x",
    "y",
    "z",
  ];

  // Convert the character into lowercase
  const myCharLowercase = myChar.toLowerCase();

  // Find the position of the char in the alphabet
  const position = letters.indexOf(myCharLowercase) + 1;

  // Return the desired message with the position
  return `Position in Alphabet: ${position}`;
}

Result

console.log(positionInAlphabet("a"));
// 1 ✅

console.log(positionInAlphabet("Z"));
// 26  ✅

Playground ⚽

You can play around with the code here

Next Part ➡️

Great work!

We learned how to use toLowerCase, charCodeAt, indexOf.

I hope you can use your new learnings to solve problems more easily!

Next time, we'll solve another interesting kata. Stay tuned!

If I should solve a specific kata, shoot me a message here.

If you want to read my latest stuff, get in touch with me!

Questions ❔

How often do you do katas?
Which implementation do you like more? Why?
Any alternative solution?

miku86