aoc-2021/day06/day06.ts

import * as A from "fp-ts/Array";
import * as N from "fp-ts/number";

import { pipe } from "fp-ts/lib/function";
import { concatAll } from "fp-ts/lib/Monoid";

import { ages as testAges } from "./input.test";
import { ages as inputAges } from "./input";

type Generations = number[];
const GEN_CYCLES = 9;
const GEN_RESTART_CYCLE = 6;
const DAYS = 256;

const parseAges = (input: string): Generations => pipe(
    input.split(","),
    A.map(parseInt),
    A.reduce(A.replicate(GEN_CYCLES, 0) as Generations, (gens, age) => A.unsafeUpdateAt(age, gens[age] + 1, gens))
);

const generations = parseAges(
    // testAges
    inputAges
);

const simulateDay = (gens: Generations): Generations => pipe(
    gens,
    A.rotate(-1),
    A.splitAt(GEN_RESTART_CYCLE),
    A.reduceWithIndex([] as Generations, (i, gens, part) => i == 0 ? part : A.concat(A.unsafeUpdateAt(0, part[0] + part[2], part))(gens))
);

const simulate = (generations: Generations, days: number): Generations => {
    if (days === 0) {
        return generations;
    }
    return simulate(simulateDay(generations), days - 1);
}

const entities = concatAll(N.MonoidSum)(simulate(generations, DAYS));
console.log(entities);