AdventOfCode-ts-2023/9/9_1.ts

import { ExtractNumbers, Inspect, LoadInput } from "../common.ts";

const tests = [
    "0 3 6 9 12 15",
    "1 3 6 10 15 21",
    "10 13 16 21 30 45",
];

const input = await LoadInput(9);

// Parse the histograms from the input
let histograms = ParseInput(input);

// Find the next predicted value for each one
histograms = histograms.map((histogram, idx) => { 
    try {
        return PredictNextValue(histogram);
    } catch (err) {
        console.error(`Failed on histogram[${idx}]`);
        throw err;
    }
});
// Sum all of the last values in the histograms
const sumOfNewValues = SumArray(histograms.map((histogram) => histogram[histogram.length - 1]));

// Wrong Answers
// 1987402315 -- too high
console.log(`The sum of all predicted values is: ${sumOfNewValues}`);

function ParseInput(inputArr: string[]): number[][] {
    return inputArr.map((historyStr) => ExtractNumbers(historyStr));
}

function PredictNextValue(histogram: number[]): number[] {
    const allDifferentials = [histogram];
    let differential = [];
    
    // Get all differentials until only an array of zeros remains
    do {
        differential = FindDifferential(allDifferentials[0]);
        allDifferentials.unshift(differential);
    } while (SumArray(differential) != 0);

    while (allDifferentials.length > 1) {
        // Store the last value of previous differential, and remove that differential from the list
        const lastValueOfDifferential = allDifferentials.shift()?.pop() as number;
        // if (lastValueOfDifferential == undefined) {
        //     throw new Error("There is no last value of previous differential!\n" + prevDifferential);
        // }
        // Store the last index of the current differential for easier reading
        const lastIndexOfDifferential = allDifferentials[0].length - 1;
        // if (lastIndexOfDifferential < 0) {
        //     throw new Error("There is no last index of the current differential");
        // }
        // Predict the next value to be this last value + the last value of the previous differential
        const predictedValue = allDifferentials[0][lastIndexOfDifferential] + lastValueOfDifferential;

        if (Number.isNaN(predictedValue)) {
            throw new Error("Failed to find differentials for the following histograms!\n" + histogram);
        }

        // Push to this differential
        allDifferentials[0].push(predictedValue);
    }

    return allDifferentials[0];
}

function FindDifferential(histogram: number[]): number[] {
    const differential: number[] = [];

    for (let i = 1; i < histogram.length; i++) {
        differential.push(histogram[i] - histogram[i - 1]);
    }

    return differential;
}

function SumArray(arr: number[]): number {
    return arr.reduce((accumulator, value) => accumulator += value, 0);
}