Advent-of-Code-2022/15/solution.mjs

import { readFileSync } from 'node:fs';

const input = readFileSync('input', 'utf-8');

const sensors = input
  .split('\n')
  .filter(Boolean)
  .map(line => {
    const match = line.match(/.*?x=(-?\d+), y=(-?\d+).*?x=(-?\d+), y=(-?\d+)/);
    if (!match) {
      throw new Error(`Invalid sensor readout: ${line}`);
    }
    const [x, y, bx, by] = match
      .slice(1)
      .map(n => parseInt(n));
    return {x, y, bx, by};
  });

function rangesOverlap(range1, range2, tollerance=0) {
  const t = tollerance;
  range1 = [...range1].sort((a, b) => a - b);
  range2 = [...range2].sort((a, b) => a - b);
  return (
    (range1[0] >= range2[0] - t && range1[0] <= range2[1] + t) ||
    (range2[0] >= range1[0] - t && range2[0] <= range1[1] + t)
  );
}

function mergeCoverage(coverage) {
  return [...coverage]
    .map(range => [...range].sort((a, b) => a - b))
    .sort((a, b) => a[0] - b[0])
    .reduce((newCoverage, range) => {
      if (newCoverage.length) {
        const lastRange = newCoverage[newCoverage.length - 1];
        if (rangesOverlap(lastRange, range, 1)) {
          newCoverage[newCoverage.length - 1] = [
            Math.min(lastRange[0], range[0]),
            Math.max(lastRange[1], range[1])
          ];
          return newCoverage;
        }
      }
      newCoverage.push(range);
      return newCoverage;
    }, []);
}

function getCoverageForRow(y) {
  const coverage = [];

  for (const s of sensors) {
    const range = Math.abs(s.x - s.bx) + Math.abs(s.y - s.by);
    const distanceToSensor = Math.abs(s.y - y);
    const reducedRange = range - distanceToSensor;

    if (reducedRange < 0) continue;

    coverage.push([s.x - reducedRange, s.x + reducedRange]);
  }

  return mergeCoverage(coverage);
}

function countBeaconsForRow(y) {
  return sensors
    .map(s => [s.bx, s.by])
    .filter((coord, i, coords) => coords.findLastIndex(
      c => c[0] === coord[0] && c[1] === coord[1]
    ) === i)
    .reduce((total, coord) => total + Number(coord[1] === y), 0);
}

function countCoverageForRow(y) {
  const coverageCount = getCoverageForRow(y)
    .reduce((total, range) => total + range[1] - range[0] + 1, 0);
  const beaconCount = countBeaconsForRow(y);
  return coverageCount - beaconCount;
}

const row = 2000000;
const coverageCount = countCoverageForRow(2000000);
console.log(
  `There are ${coverageCount} positions that cannot contain a beacon on ` +
    `row: ${row}`
);


function limitCoverage(coverage, min, max) {
  return coverage
    .filter(range => rangesOverlap([min, max], range))
    .map(range => [Math.max(min, range[0]), Math.min(max, range[1])]);
}

console.log('Locating distress beacon...');
let tuningFrequency;
for (let y = 0; y <= 4000000; y++) {
  const coverage = limitCoverage(getCoverageForRow(y), 0, 4000000);
  if (coverage.length > 1) {
    const x = coverage[0][1] + 1;
    tuningFrequency = x * 4000000 + y;
  }
}
console.log(`Tuning frequency for distress beacon: ${tuningFrequency}`);