82 lines
2.2 KiB
D
82 lines
2.2 KiB
D
import std.stdio;
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import std.algorithm;
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import std.string;
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import std.array;
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import std.math;
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struct Node {
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string name, left, right;
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}
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struct Puzzle {
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string instructions;
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Node[string] nodes;
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}
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Puzzle parsePuzzle(string filename) {
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Puzzle p;
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string[] lines = File(filename).byLineCopy.array;
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p.instructions = lines[0].strip;
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foreach (string line; lines[2..$]) {
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string[] nameAndBranches = line.split("=");
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string name = nameAndBranches[0].strip;
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string[] branches = nameAndBranches[1].strip[1..$-1].split(",").map!strip.array;
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p.nodes[name] = Node(name, branches[0], branches[1]);
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}
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return p;
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}
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void part1() {
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Puzzle p = parsePuzzle("input.txt");
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Node currentNode = p.nodes["AAA"];
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size_t instructionIdx = 0;
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ulong steps = 0;
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while (currentNode.name != "ZZZ") {
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char instruction = p.instructions[instructionIdx++];
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if (instructionIdx >= p.instructions.length) instructionIdx = 0;
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if (instruction == 'L') {
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currentNode = p.nodes[currentNode.left];
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} else if (instruction == 'R') {
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currentNode = p.nodes[currentNode.right];
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}
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steps++;
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}
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writeln(steps);
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}
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void part2() {
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ulong gcd(ulong a, ulong b) {
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if (a < b) swap(a, b);
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while (b != 0) {
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a = a % b;
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swap(a, b);
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}
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return a;
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}
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ulong lcm(ulong a, ulong b) {
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return a / gcd(a, b) * b;
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}
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Puzzle p = parsePuzzle("input.txt");
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Node[] startNodes = p.nodes.values.filter!(n => n.name[$-1] == 'A').array;
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ulong lcmSteps = 1;
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foreach (size_t i, Node startNode; startNodes) {
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Node currentNode = startNode;
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ulong cycleLength = 0;
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size_t instructionIdx = 0;
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while (currentNode.name[$-1] != 'Z') {
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char instruction = p.instructions[instructionIdx++];
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if (instructionIdx >= p.instructions.length) instructionIdx = 0;
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currentNode = instruction == 'L' ? p.nodes[currentNode.left] : p.nodes[currentNode.right];
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cycleLength++;
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}
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lcmSteps = lcm(lcmSteps, cycleLength);
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}
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writeln(lcmSteps);
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}
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void main() {
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part1();
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part2();
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}
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