readme.md

Challenge: Sum of Squares of Even Numbers

Instructions

Let's start off with a fairly simple challenge, but one that uses a few different array methods. Write a function called sumOfEvenSquares that takes an array of numbers and returns the sum of the squares of the even numbers in the array.

Function Signature

/**
 * Returns the sum of the squares of the even numbers in the array.
 * @param {number[]} numbers - The array of numbers.
 * @returns {number} - The sum of the squares of even numbers.
 */
function sumOfEvenSquares(numbers: number[]): number

Examples

sumOfEvenSquares([1, 2, 3, 4, 5]); // 20 (2^2 + 4^2)
sumOfEvenSquares([-1, 0, 1, 2, 3, 4]); // 20 (0^2 + 2^2 + 4^2)
sumOfEvenSquares([]); // 0

Hints

• Use the filter method to select the even numbers from the array.
• Then, use the map method to square each even number.
• Finally, use the reduce method to sum up the squared even numbers.

Solutions

Click For Solution

function sumOfEvenSquares(numbers) {
  const evenSquares = numbers
    .filter((num) => num % 2 === 0)
    .map((num) => num ** 2);

  return evenSquares.reduce((sum, square) => sum + square, 0);
}

Explanation

You can format this so many different ways. This is just one example.

• Create a variable called evenSquares and set it equal to the result of calling the filter method on the numbers array and then calling the map method on the result of that.

• For the filter method, pass in a callback function that takes in a number and returns true if the number is even and false otherwise. We used the modulo operator (%) to check if the number is even.

• For the map method, pass in a callback function that takes in a number and returns the square of that number. Now we have an array of the squares of the even numbers.

• Finally, call the reduce method on the evenSquares array and pass in a callback function that takes in a sum and a square and returns the sum plus the square. We set the initial value of the sum to 0.

We could even shorten this by chaining the methods together and using an arrow function:

const sumOfEvenSquares = (numbers) =>
  numbers
    .filter((num) => num % 2 === 0)
    .map((num) => num ** 2)
    .reduce((sum, square) => sum + square, 0);

Test Cases

test('Sum of even squares', () => {
  expect(sumOfEvenSquares([1, 2, 3, 4, 5])).toBe(20);
  expect(sumOfEvenSquares([-1, 0, 1, 2, 3, 4])).toBe(20);
  expect(sumOfEvenSquares([])).toBe(0);
});