expeditaet/solutions/typescript/2021/21/src/p2.ts

Advent of Code Solutions

/* eslint-disable @typescript-eslint/no-non-null-assertion */
import { memoize, numberPair, task } from '@alexaegis/advent-of-code-lib';
import packageJson from '../package.json';

interface RoundState {
	p1Position: number;
	p2Position: number;
	p1Score: number;
	p2Score: number;
	rollPhase: number;
	isP1Turn: boolean;
}

interface RoundResultState {
	p1WinCount: number;
	p2WinCount: number;
}

const playFromRoundState = memoize(
	(state: RoundState, roll: number): RoundResultState => {
		const nextState: RoundState = { ...state };
		if (nextState.isP1Turn) {
			nextState.p1Position = nextState.p1Position.addWithinRange(roll, 1, 10);
		} else {
			nextState.p2Position = nextState.p2Position.addWithinRange(roll, 1, 10);
		}

		if (nextState.rollPhase === 2) {
			if (nextState.isP1Turn) {
				nextState.p1Score += nextState.p1Position;
			} else {
				nextState.p2Score += nextState.p2Position;
			}
		}

		if (nextState.p1Score >= 21) {
			return { p1WinCount: 1, p2WinCount: 0 };
		} else if (nextState.p2Score >= 21) {
			return { p1WinCount: 0, p2WinCount: 1 };
		} else {
			nextState.rollPhase++;
			if (nextState.rollPhase > 2) {
				nextState.rollPhase = 0;
				nextState.isP1Turn = !nextState.isP1Turn;
			}
			return diracRoll(nextState);
		}
	},
	{ maxCacheEntries: Number.POSITIVE_INFINITY },
);

const diracRoll = (state: RoundState): RoundResultState => {
	const result1 = playFromRoundState(state, 1);
	const result2 = playFromRoundState(state, 2);
	const result3 = playFromRoundState(state, 3);

	return {
		p1WinCount: result1.p1WinCount + result2.p1WinCount + result3.p1WinCount,
		p2WinCount: result1.p2WinCount + result2.p2WinCount + result3.p2WinCount,
	};
};

export const parse = (line: string): number => {
	const [, position] = line.match(/\d/g)!;
	return Number.parseInt(position!, 10);
};

export const p2 = (input: string): number => {
	const [p1Position, p2Position] = numberPair.assert(input.lines().map(parse));
	const result = diracRoll({
		p1Position,
		p2Position,
		p1Score: 0,
		p2Score: 0,
		isP1Turn: true,
		rollPhase: 0,
	});
	return Object.values(result).max();
};

await task(p2, packageJson.aoc); // 4184 ~0.0036ms