part2.ts

import * as fs from 'fs';
const input = fs.readFileSync('input', 'utf8').split('\n');

let result = 0;

for (const line of input) {
	const values = line.split(' ').map((x) => Number(x));
	const differences = [[...values]];
	while (differences[differences.length - 1].some((x) => x != 0)) {
		differences.push(differences[differences.length - 1].map((x, i, r) => x - r[i - 1]).slice(1));
	}

	let firstNumbers = differences.map((x) => x[0]);
	firstNumbers = firstNumbers.map((x, i) => (i % 2 === 1 ? -x : x)); // reverse sign for odd indices

	result += firstNumbers.reduce((a, b) => a + b);
}

console.log(result);