Programming-related ideas and writings.

Calorie Counting

Mar 25, 2024

Part One

This problem is all about elves and how many Calories they are carrying in their inventories. With that said, let's first set up a simple test that captures the domain language and ensures we can add Calories to an elf's inventory. In a business sense, we are primarily concerned with the total number of Calories, so we'll capture that in the test.

Here is what our test code might look like:

import { expect, test } from 'bun:test';
import { Elf } from './Elf';

test("that elf's inventory tracks Calories", () => {
    const elf = new Elf();

In this test, we instantiate an Elf and add a couple of Calorie counts to their inventory. At the end, we expect all of those Calories to be added up and reported by the totalCalories property.

Now that that's done, we can implement our actual Elf class.

export class Elf {
    private _totalCalories = 0;

    get totalCalories() {
        return this._totalCalories;

    addToInventory = (calories: number) => {
        this._totalCalories += calories;

Now we can see that the test passes:

bun test v1.0.8 (2a405f69)

✓ that elf's inventory tracks Calories [0.06ms]

 1 pass
 0 fail
 1 expect() calls
Ran 1 tests across 1 files. [8.00ms]

This is great, but there's still a lot missing. We need to parse some input and get a list of inventory-filled elves. For that, we can write a test using the example input from the problem.

import { expect, test } from 'bun:test';
import { parseInventoryList } from './parseInventoryList';

const TEXT = `1000





test('that list is created', () => {
    const elves = parseInventoryList(TEXT);

And from that, we can make a simple function that handles the input parsing.

import { Elf } from './Elf';

export function parseInventoryList(text: string): Array<Elf> {
    const elves = new Array<Elf>();
    const elfInventories = text.split('\n\n');
    for (let inventory of elfInventories) {
        const elf = new Elf();
            .map((n) => Number.parseInt(n, 10))
    return elves;

Packaging up the code like this carries the benefit of leaving a very simple script to solve the problem. For example, it could look something like this:

const elves = parseInventoryList(input);
const maxCalorieElf = elves.reduce((max, curr) =>
    curr.totalCalories > max.totalCalories ? curr : max

Now, is this overkill? Yes. It's quite obvious that all we're being asked to do in this problem is sum some numbers and determine a max, but what I hope to illustrate is that, had this been more complex, we've laid a pretty good foundation for understanding. When we look at the code snippet above, I think it's pretty clear what is being done. In fact, we've left a little work that could be done in this area. The elves.reduce call just doesn't read very well. It's not immediately clear what it's doing. Let's clear that up by refactoring that portion to a named function.

const elves = parseInventoryList(input);
const elf = findElfWithMostCalories(elves);

function findElfWithMostCalories(elves: Array<Elf>) {
    return elves.reduce((max, curr) =>
        curr.totalCalories > max.totalCalories ? curr : max

This reads much better. Even without reading the problem text, we can tell that the goal of this code is:

  1. Parse the input into a list of elves.
  2. Find the elf with the most Calories.
  3. Display that number.

Part Two

Part two of the day 1 problem set is only a minor change. Rather than getting the elf with the most Calories, we need to get the top three. This is a pretty easy change. We can simply sort the list of elves by the Calorie counts in descending order and then grab the first three elves from the array. Lucky for us, there's no domain changes here.

const elves = parseInventoryList(input);
const top3 = findTop3ElvesWithMostCalories(elves);
const total = sumElfCalories(top3);

function findTop3ElvesWithMostCalories(elves: Array<Elf>) {
    return elves
        .sort((a, b) => (a.totalCalories < b.totalCalories ? 1 : -1))
        .slice(0, 3);

function sumElfCalories(elves: Array<Elf>) {
    return elves.reduce((sum, elf) => sum + elf.totalCalories, 0);