AdventOfCode-js-2024/2/2_1.js

import { loadInput, numericAscSort, strToInt } from "../common.js";

// const input = loadInput("./2/test.input", parseInput, true);
const input = loadInput(2, parseInput);

solve(input);

/**
 * @param {string} inputData
 * @returns {number[]}
 */
function parseInput(inputData) {
    const reports = inputData.split(/\n/).map((report) => report.split(" ").map(strToInt));

    return reports;
}

/**
 * @param {number[]} parsedInput 
 */
function solve(parsedInput) {
    let safeReports = 0;

    for(const report of parsedInput) {
        let currDirection = 0;
        let lastDirection = 0;
        /**
         * Whether or not the report is safe
         * 
         * Report is only safe when the data is sorted in one direction, and
         * each value is no less than 1 value away, and no more than 3 values
         * away from each other.
         *
         * e.g.
         * ```
         * 1,2,3,4,5    safe
         * 5,4,3,2,1    safe
         * 1,2,3,2,1    unsafe
         * 1,2,4,5,6    safe
         * 1,2,7,8,9    unsafe
         * ```
         */
        let safe = false;

        // Safety check written this way to make troubleshooting easier
        for(let i = 0; i < report.length - 1; i++) {
            currDirection = numericAscSort(report[i], report[i + 1]);
            const difference = Math.abs(report[i] - report[i + 1]);

            // Check if the direction has changed, but skip the first round
            // Also catches if there were no differences between the two numbers
            if(i != 0 && lastDirection != currDirection) {
                safe = false;
                break;
            }
            // Make sure the difference wasn't too great
            else if(difference > 3) {
                safe = false;
                break;
            }
            else {
                safe = true;
            }

            lastDirection = currDirection;
        }

        if(safe) { safeReports++; }
    }

    // Not: ^400, ^391
    console.log("Safe Reports:", safeReports);
}