Advent of Code 2020 Day 1 TypeScript

day1.ts

import { readFileSync } from 'fs';

const expenses = readFileSync('input.txt').toString('utf8').split('\n').map(n => parseInt(n));

const threeNumberSumIndices = (numbers: number[], targetSum: number) : [number, number, number] | null=> {
    let first, second, third;
    for (let i = 0; i < numbers.length; i++) {
        first = numbers[i];
        for (let j = i + 1; j < numbers.length; j++) {
            second = numbers[j];
            for (let k = i + 1; k < numbers.length; k++) {
                third = numbers[k];
                if (first + second + third === targetSum) {
                    return [i, j, k];
                }
            }
        }
    }

    return null;
}

/**
 * Finds the indices of two numbers adding up to `targetSum` in a list of numbers. Returns `null` if
 * no combination of two numbers is found
 * @param numbers The list of numbers in which to find indices
 * @param targetSum The sum to find two numbers adding up to
 */
const twoNumberSumIndices = (numbers: number[], targetSum: number) : [number, number] | null=> {
    let currentLHS, currentRHS;
    for (let i = 0; i < numbers.length; i++) {
        currentLHS = numbers[i];
        for (let j = i + 1; j < numbers.length; j++) {
            currentRHS = numbers[j];
            if (currentLHS + currentRHS === targetSum) {
                return [i, j];
            }
        }
    }

    return null;
}

const twoIndices = twoNumberSumIndices(expenses, 2020);
if (twoIndices) {
    const [lhs, rhs] = twoIndices;
    console.log("Chapter 1", expenses[lhs] * expenses[rhs]);
} else {
    throw new Error('No indices found');
}

const threeIndices = threeNumberSumIndices(expenses, 2020);
if (threeIndices) {
    const [first, second, third] = threeIndices;
    console.log("Chapter 2", expenses[first] * expenses[second] * expenses[third]);
} else {
    throw new Error('No indices found');
}