JavaScript Katas: Calculate total amount of points

2020-07-14

Intro 🌐

I take interesting katas of all levels and explain how to solve them.

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

You'd better learn to solve problems!

Source

I take the ideas for the katas from different sources and re-write them.

Today's source: Codewars

Understanding the Exercise ❗

First, we need to understand the exercise!

This is a crucial part of (software) engineering.

Go over the exercise explanation again until you understand it 100%.

Do NOT try to save time here.

My method to do this:

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

Today's exercise

Write a function calculateAmountOfPoints, that accepts one parameter: games, a valid array of strings, e.g. ["3:1", "2:2"].

Points:

x > y: 3 points
x = y: 1 point
x < y: 0 point

The function should return a number. The number is the sum of the point(s) of every single game.

Input: an array of strings.

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.

loop over every element of the games array
calculate the specific score of this element
return the sum of every single element (a number)

Example:

Input: ["3:1", "2:2"]
Iteration 1: "3:1" // x > y => 3 points
Iteration 2: "2:2" // x = y => 1 point
Output: 4 // return the sum (3 + 1) as a number

Implementation (for of-loop) ⛑

function calculateAmountOfPoints(games) {
  // counter for total points
  let totalPoints = 0;

  for (const game of games) {
    // split the game score for both teams and assign it to two variables
    const [scoreA, scoreB] = game.split(":");

    // calculate the points for this game with a ternary operator
    const points = scoreA > scoreB ? 3 : scoreA === scoreB ? 1 : 0;

    // add the points for this specific game to the total points
    totalPoints += points;
  }

  return totalPoints;
}

Result

console.log(calculateAmountOfPoints(["3:1", "2:2"]));
// 4

console.log(calculateAmountOfPoints(["1:0", "2:0", "3:0", "4:0", "2:1"]));
// 15

Implementation (functional) ⛑

function calculateAmountOfPoints(games) {
  return (
    games
      // split the game score into two separate values
      .map((game) => game.split(":"))

      // calculate the points for this game with a ternary operator
      .map((score) => (score[0] > score[1] ? 3 : score[0] === score[1] ? 1 : 0))

      // calculate the sum of all games
      .reduce((acc, cur) => acc + cur, 0)
  );
}

Result

console.log(calculateAmountOfPoints(["3:1", "2:2"]));
// 4

console.log(calculateAmountOfPoints(["1:0", "2:0", "3:0", "4:0", "2:1"]));
// 15

Playground ⚽

You can play around with the code here

Next Part ➡️

Great work, mate!

Next time, we'll solve the next 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 ❔

Do you like to solve katas?
Which implementation do you like more? Why?
Any alternative solution?

miku86