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miku86
miku86

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JavaScript Katas: Count lowercase letters

#javascript #beginners #webdev #codenewbie

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:

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

Today's exercise

Source: Codewars

Write a function amountOfLowercaseLetters, that accepts one parameter: inputString.

Given a string, e.g. "aB1c",
return the number of lowercase letters in this string, e.g. 2:

Input: a string.

Output: a number.

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.

  1. Loop over every character
  2. Check if it is a lowercase letter
  3. If yes, then increase count of lowercase letters by 1
  4. Return count of lowercase letters

Example:

  • Input: "aB1c"
  • Iteration 1: lowercase letter? true => Increase count of lowercase letters by 1
  • Iteration 2: lowercase letter? false => Do nothing
  • Iteration 3: lowercase letter? false => Do nothing
  • Iteration 4: lowercase letter? true => Increase count of lowercase letters by 1
  • Output: 2 (count of lowercase letters) ✅

Implementation (for) ⛑ 

function amountOfLowercaseLetters(inputString) { let count = 0; // loop over every char for (const char of inputString) { // check if it is lowercase if (char.match(/[a-z]/)) { // if yes, increase count count += 1; } } return count; }
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Result 

console.log(amountOfLowercaseLetters("aB1c")); // 2 ✅ console.log(amountOfLowercaseLetters("123")); // 0 ✅
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Implementation (functional) ⛑ 

function amountOfLowercaseLetters(inputString) { return inputString .split("") // convert into array .filter((char) => char.match(/[a-z]/)) // filter out all lowercase chars .length; // take the length }
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Result 

console.log(amountOfLowercaseLetters("aB1c")); // 2 ✅ console.log(amountOfLowercaseLetters("123")); // 0 ✅
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Implementation (global regex) ⛑ 

function amountOfLowercaseLetters(inputString) { return (inputString.match(/[a-z]/g) || []).length; }
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We use the g flag to return all matches. Because null would get returned if there wouldn't be a match, we add an [] to use length.

Result 

console.log(amountOfLowercaseLetters("aB1c")); // 2 ✅ console.log(amountOfLowercaseLetters("123")); // 0 ✅
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Playground ⚽

You can play around with the code here

Next Part ➡️

Great work!

We learned how to use for of, match, filter and length.

I hope that 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!

Further Reading 📖

Questions ❔

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

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