aoc-2021/day09/day09.ts

import * as A from "fp-ts/Array";
import * as RA from "fp-ts/ReadonlyArray";
import * as S from "fp-ts/string";
import * as N from "fp-ts/number";

import { flow, pipe } from "fp-ts/lib/function";
import { heightmap }  from "./input";
// import { heightmap } from "./input.test";
import { concatAll } from "fp-ts/lib/Monoid";


type HeightMap = ReadonlyArray<ReadonlyArray<number>>;
const parseHeightMap = (input: string): HeightMap => pipe(
    input,
    S.split("\n"),
    RA.map(flow(S.split(""), RA.map(parseInt)))
);

const localMinima = (heightMap: HeightMap): number[] => {
    const minima: number[] = [];
    for (let i = 0; i < heightMap.length; i++) {
        for (let j = 0; j < heightMap[i].length; j++) {
            const up = heightMap[i - 1]?.[j] ?? Number.MAX_VALUE;
            const down = heightMap[i + 1]?.[j] ?? Number.MAX_VALUE;
            const left = heightMap[i]?.[j - 1] ?? Number.MAX_VALUE;
            const right = heightMap[i]?.[j + 1] ?? Number.MAX_VALUE;
            const value = heightMap[i][j];
            if (value < up && value < down && value < left && value < right) {
                minima.push(value);
            }
        }
    }
    return minima;
}

const sumOfRiskLevels = pipe(
    parseHeightMap(heightmap),
    localMinima,
    A.map(n => n + 1),
    concatAll(N.MonoidSum)
);

console.log(sumOfRiskLevels);