math & informatics teacher
sample = `
0 3 6 9 12 15
1 3 6 10 15 21
10 13 16 21 30 45
`
parsed = input
.trim()
.split("\n")
.map((l) => l.split(" ").map(Number))
parsed[0]
function differences(list) {
const stack = [list];
while (!stack.at(-1).every((d) => d === 0))
stack.push(d3.pairs(stack.at(-1)).map(([a, b]) => b - a));
return stack;
}
function after(list) {
let n = 0;
for (let r of differences(list).reverse().slice(1)) {
n = r.at(-1) + n;
}
return n;
}
part1 = parsed.map(after).reduce((sum, n) => sum + n)
function before(list) {
let n = 0;
for (let r of differences(list).reverse().slice(1)) {
n = r[0] - n;
}
return n;
}
part2 = parsed.map(before).reduce((sum, n) => sum + n)
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