tasks.mjs

// Floodfilling.

import input from './input.mjs';

// const input = [2199943210,3987894921,9856789892,8767896789,9899965678]

const map = input.map((x) => [...x.toString()]);

// Task 1 identifies lowest poiints, and adds their score together

function task1(map) {
  const lowestPoints = map.flatMap((row, y) => {
    return row.filter((cell, x) => {
      const offsets = [
        [0, 1],
        [1, 0],
        [0, -1],
        [-1, 0],
      ];
      return offsets.every((offset) => {
        const x2 = x + offset[0];
        const y2 = y + offset[1];
        if (x2 < 0 || y2 < 0 || x2 >= map[0].length || y2 >= map.length) {
          return true;
        }
        return map[y2][x2] > cell;
      });
    });
  });
  return lowestPoints.reduce(
    (acc, point) => acc + 1 + Number.parseInt(point),
    0,
  );
}

console.log(task1(map));

// task 2 finds the lowest points, and then backfills them up to points at height 9 and determines the size of the area

function task2(map) {
  const mapObjects = objectifyMap(map);
  const lowestPoints = findLowestPoints(mapObjects);
  const basins = lowestPoints.map((point) => {
    return flood(mapObjects, ...point);
  });
  const largestBasins = basins.sort((a, b) => b - a).slice(0, 3);

  displayMap(mapObjects);
  return largestBasins.reduce((acc, basin) => acc * basin);
}

function objectifyMap(map) {
  return map.map((row) => {
    return row.map((cell) => {
      return {
        height: cell,
        filled: false,
      };
    });
  });
}

function findLowestPoints(map) {
  const lowestPoints = map.flatMap((row, y) => {
    return row.reduce((acc, cell, x) => {
      const offsets = [
        [0, 1],
        [1, 0],
        [0, -1],
        [-1, 0],
      ];
      if (
        offsets.every((offset) => {
          const x2 = x + offset[0];
          const y2 = y + offset[1];
          if (x2 < 0 || y2 < 0 || x2 >= map[0].length || y2 >= map.length) {
            return true;
          }
          return map[y2][x2].height > cell.height;
        })
      )
        acc.push([y, x]);
      return acc;
    }, []);
  });
  return lowestPoints;
}

function flood(map, y, x) {
  if (map[y][x].filled) return 0;
  if (map[y][x].height >= 9) return 0;
  map[y][x].filled = true;
  const offsets = [
    [0, 1],
    [1, 0],
    [0, -1],
    [-1, 0],
  ];
  return offsets.reduce((acc, offset) => {
    const x2 = x + offset[0];
    const y2 = y + offset[1];
    if (x2 < 0 || y2 < 0 || x2 >= map[0].length || y2 >= map.length) {
      return acc;
    }
    return acc + flood(map, y2, x2);
  }, 1);
}

function displayMap(map) {
  let string = '\n\n';
  map.forEach((row) => {
    row.forEach((cell) => {
      if (cell.filled) {
        string += '\x1b[34m#\x1b[89m';
      } else {
        string += `\x1b[97m${cell.height}\x1b[39m`;
      }
    });
    string += '\n';
  });
  console.clear();
  console.log(string);
}

console.time('task2');
console.log(task2(map));
console.timeEnd('task2');