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day-9.js
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day-9.js
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const fs = require('fs');
const fileName = "data/day-9-input.txt";
const file = fs.readFileSync(fileName, 'utf8');
const lines = file.split(/\r?\n/);
function isRootSequence(sequence) {
let isRoot = true;
for(let i = 0; i < sequence.length; i++) {
if (sequence[i] != 0) {
isRoot = false;
break;
}
}
return isRoot;
}
function findDifferenceSequence(sequence) {
let differences = [];
for(let i = 0; i < sequence.length - 1; i++) {
differences.push(sequence[i + 1] - sequence[i]);
}
return differences;
}
function findNextSequenceElement(sequence) {
let derrivatives = [];
derrivatives.push(sequence);
let rootFound = false;
while(!rootFound) {
if (isRootSequence(derrivatives[derrivatives.length - 1])) {
rootFound = true;
break;
}
let differences = findDifferenceSequence(derrivatives[derrivatives.length - 1]);
derrivatives.push(differences);
}
// Solve for the next number
for(let i = derrivatives.length - 1; i > 0; i--) {
let nextNumber = derrivatives[i][derrivatives[i].length - 1] + derrivatives[i - 1][derrivatives[i - 1].length - 1];
derrivatives[i - 1].push(nextNumber);
}
return derrivatives[0][derrivatives[0].length - 1];
}
let nextItems = [];
for(let i = 0; i < lines.length; i++) {
let sequence = lines[i].split(" ").map(x => Number(x));
let nextItem = findNextSequenceElement(sequence);
nextItems.push(nextItem);
}
let finalAnswer = nextItems.reduce((acc, cur) => {
return acc + cur;
}, 0);
console.log(`Part 1: ${finalAnswer}`);
let previousItems = [];
for(let i = 0; i < lines.length; i++) {
let sequence = lines[i].split(" ").map(x => Number(x)).reverse();
let previousItem = findNextSequenceElement(sequence);
previousItems.push(previousItem);
}
let finalAnswer2 = previousItems.reduce((acc, cur) => {
return acc + cur;
}, 0);
console.log(`Part 2: ${finalAnswer2}`);