adventofcode/2022/12/part2.js

import * as R from "remeda";
import Victor from "@a-robu/victor";

import { readFile } from "../05/part1.js";

const V = (x, y) => new Victor(x, y);

export const findAs = (topoMap) => {
  const locations = [];

  topoMap.forEach((line, x) =>
    line.forEach((v, y) => {
      if (v === "a") locations.push([x, y]);
    })
  );

  return locations;
};

export const findEnd = (topoMap) => {
  let y;
  let x = R.findIndex(topoMap, (row) => {
    let z = row.indexOf("E");
    if (z === -1) return false;
    y = z;
    return true;
  });
  return V(x, y);
};

const directions = [
  [0, 1],
  [0, -1],
  [1, 0],
  [-1, 0],
].map((d) => V(...d));

const outOfMap = (maxX, maxY) => (loc) => {
  if (Math.min(loc.x, loc.y) < 0) return true;
  if (loc.x >= maxX) return true;
  if (loc.y >= maxY) return true;
  return false;
};

const isReachable = (topoMap, pos) => {
  const baseline = topoMap[pos.x][pos.y].charCodeAt(0);

  return (next) => {
    return baseline - topoMap[next.x][next.y].charCodeAt(0) <= 1;
  };
};

function findShortestPath(topoMap) {
  const final = findEnd(topoMap);
  final.steps = 0;

  topoMap = topoMap.map((line) =>
    line.map((c) => c.replace("S", "a").replace("E", "z"))
  );

  const initial = findAs(topoMap);

  const potentials = [final];

  const beenThere = topoMap.map((line) => line.map(() => 9999));

  const oom = outOfMap(topoMap.length, topoMap[0].length);

  let failsafe = 10; //topoMap.length*topoMap[0].length ;
  while (potentials.length > 0) {
    //    if(! failsafe--) return;
    const pos = potentials.shift(); // depth-first

    if (beenThere[pos.x][pos.y] <= pos.steps) continue;
    beenThere[pos.x][pos.y] = pos.steps;

    const next = directions
      .map((d) => d.clone().add(pos))
      .filter(R.isNot(oom))
      .filter(isReachable(topoMap, pos));

    next.forEach((n) => (n.steps = pos.steps + 1));

    potentials.push(...next);
  }

  return R.pipe(
    initial,
    R.map(([x, y]) => beenThere[x][y]),
    R.minBy(R.identity)
  );
}

export default findShortestPath;