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import fs from "fs";
function gcd(a: number, b: number) {
return !b ? a : gcd(b, a % b);
}
function lcm(a: number, b: number) {
return (a * b) / gcd(a, b);
}
const [directions, _, ...lines] = fs
.readFileSync("./input.txt")
.toString()
.split("\n")
.slice(0, -1);
const nodes = lines
.map((line) => {
const match = line.match(/(...) = \((...), (...)\)/);
if (!match) throw new Error("Could not match");
return {
node: match[1],
left: match[2],
right: match[3],
};
})
.map((node, index, nodes) => ({
name: node.node,
node: index,
left: nodes.findIndex((n) => n.node === node.left),
right: nodes.findIndex((n) => n.node === node.right),
}));
const [startingNodes, terminalNodes] = ["A", "Z"].map((char) =>
nodes.filter((n) => n.name.endsWith(char)).map((n) => n.node),
);
const result = startingNodes
.map((node) => {
let steps = 0;
while (!terminalNodes.includes(node)) {
const direction = (
{
L: "left",
R: "right",
} as const
)[directions[steps % directions.length]];
if (!direction) throw new Error("Invalid direction");
node = nodes[node][direction];
steps++;
}
return steps;
})
.reduce((acc, x) => lcm(acc, x), 1);
console.log({ result });
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