Day Eight: Part Two

This commit is contained in:
Lewis Dale 2023-12-08 10:04:45 +00:00
parent 35f5601f1e
commit c86bcbffb6
2 changed files with 74 additions and 6 deletions

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@ -1,4 +1,4 @@
import {DesertMap} from "./day_eight"; import {DesertMap, lcm} from "./day_eight";
describe('Day Eight', () => { describe('Day Eight', () => {
const input = `RL const input = `RL
@ -17,6 +17,17 @@ AAA = (BBB, BBB)
BBB = (AAA, ZZZ) BBB = (AAA, ZZZ)
ZZZ = (ZZZ, ZZZ)` ZZZ = (ZZZ, ZZZ)`
const ghostInput = `LR
11A = (11B, XXX)
11B = (XXX, 11Z)
11Z = (11B, XXX)
22A = (22B, XXX)
22B = (22C, 22C)
22C = (22Z, 22Z)
22Z = (22B, 22B)
XXX = (XXX, XXX)`
it('should calculate the number of steps needed to reach ZZZ', () => { it('should calculate the number of steps needed to reach ZZZ', () => {
const map = new DesertMap(input); const map = new DesertMap(input);
expect(map.stepsTo('ZZZ')).toEqual(2); expect(map.stepsTo('ZZZ')).toEqual(2);
@ -25,5 +36,16 @@ ZZZ = (ZZZ, ZZZ)`
it('should repeat the pattern', () => { it('should repeat the pattern', () => {
const map = new DesertMap(repeatedInput); const map = new DesertMap(repeatedInput);
expect(map.stepsTo('ZZZ')).toEqual(6); expect(map.stepsTo('ZZZ')).toEqual(6);
}) });
it('should count how many steps it takes to get from every node beginning with A, to every node ending in Z simultaneously', () => {
const map = new DesertMap(ghostInput);
expect(map.ghostStepsToZ()).toEqual(6);
});
describe('lcm', () => {
it('should get the correct lowest common multiple', () => {
expect(lcm(12, 30)).toEqual(60);
});
});
}); });

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@ -1,10 +1,11 @@
import {anyCharOf, newline, uniLetter, whitespace} from "parjs"; import {anyCharOf, int, newline, uniDecimal, uniLetter, whitespace} from "parjs";
import {between, exactly, manySepBy, manyTill, stringify, then} from "parjs/combinators"; import {between, exactly, manySepBy, manyTill, or, stringify, then} from "parjs/combinators";
import fs from "fs"; import fs from "fs";
import { Set } from 'immutable';
const patternParser = anyCharOf("LR").pipe(manyTill(newline().pipe(exactly(2)))); const patternParser = anyCharOf("LR").pipe(manyTill(newline().pipe(exactly(2))));
const nodeNameParser = uniLetter().pipe(exactly(3), stringify()); const nodeNameParser = uniLetter().pipe(or(uniDecimal()), exactly(3), stringify());
const childParser = nodeNameParser.pipe(manySepBy(", "), exactly(2), between("(", ")")); const childParser = nodeNameParser.pipe(manySepBy(", "), exactly(2), between("(", ")"));
const nodeParser = nodeNameParser.pipe(then(childParser.pipe(between(" = ", whitespace())))) const nodeParser = nodeNameParser.pipe(then(childParser.pipe(between(" = ", whitespace()))))
@ -16,6 +17,16 @@ type Instruction = "L" | "R";
type NodeName = string; type NodeName = string;
type NodeChildren = [Maybe<NodeName>, Maybe<NodeName>]; type NodeChildren = [Maybe<NodeName>, Maybe<NodeName>];
const gcd = (a: number, b: number): number => {
if (b === 0) return a;
return gcd(b, a % b);
}
export const lcm = (a: number, b: number): number => {
const product = a * b;
return product / gcd(a, b);
}
export class DesertMap { export class DesertMap {
private readonly pattern: Instruction[]; private readonly pattern: Instruction[];
@ -30,7 +41,7 @@ export class DesertMap {
if (!this.map[name]) { if (!this.map[name]) {
this.map[name] = [undefined, undefined]; this.map[name] = [undefined, undefined];
} }
const children = [leftNode !== name ? leftNode : undefined, rightNode !== name ? rightNode : undefined]; const children = [leftNode, rightNode];
this.map[name] = children as NodeChildren; this.map[name] = children as NodeChildren;
} }
} }
@ -56,11 +67,46 @@ export class DesertMap {
} }
return step; return step;
} }
public stepsToZ(from: string): number {
let step = 0;
let curr = from;
while (!curr.endsWith('Z')) {
const instruction = this.pattern[step % this.pattern.length];
const [left, right] = this.map[curr];
if (instruction === "L" && left) {
curr = left;
} else if (instruction === "R" && right) {
curr = right;
} }
if (!curr) return 0;
step++;
}
return step;
}
private isComplete(keys: string[]) {
return keys.every(key => key.endsWith('Z'));
}
public ghostStepsToZ(): number {
let keys = Object.keys(this.map).filter(key => key.endsWith('A'));
return keys.map(key => this.stepsToZ(key)).reduce(lcm, 1);
}
}
export const runDayEight = () => { export const runDayEight = () => {
const input = fs.readFileSync('./inputs/day_eight_input.txt', 'utf-8').trimEnd(); const input = fs.readFileSync('./inputs/day_eight_input.txt', 'utf-8').trimEnd();
const map = new DesertMap(input); const map = new DesertMap(input);
console.log(map.stepsTo('ZZZ')); console.log(map.stepsTo('ZZZ'));
console.log(map.ghostStepsToZ());
} }