Advent of Code Day 2022 - Day 12

advent-of-code-2022-12.js

const INPUT = `...`;

console.log(findPathDistance("S", "E")); // Part 1
console.log(findPathDistance("E", "a", true)); // Part 2

function findPathDistance(startChar, endChar, isReverse = false) {
  const { grid, start } = parseInput(startChar);
  const q = [[...start, 0]];
  const visited = new Set();
  return findPath();

  function findPath() {
    for (let i = 0; i < q.length; i++) {
      const [x, y, d] = q[i];
      if (visited.has([x, y].join(","))) continue;
      if (grid[x][y] === endChar) return d;
      visited.add([x, y].join(","));
      const neighbors = getNeighbors(x, y);
      q.push(...neighbors.map(([x, y]) => [x, y, d + 1]));
    }
  }

  function parseInput(startChar) {
    const grid = [];
    let start = [0, 0];
    INPUT.split(/\n/).forEach((line, y) => {
      line.split("").forEach((char, x) => {
        grid[x] = grid[x] || [];
        grid[x].push(char);
        if (char === startChar) start = [x, y];
      });
    });
    return { grid, start };
  }

  function getNeighbors(x, y) {
    const neighbors = [];
    if (isWalkable(x, y - 1, grid[x][y])) neighbors.push([x, y - 1]);
    if (isWalkable(x, y + 1, grid[x][y])) neighbors.push([x, y + 1]);
    if (isWalkable(x - 1, y, grid[x][y])) neighbors.push([x - 1, y]);
    if (isWalkable(x + 1, y, grid[x][y])) neighbors.push([x + 1, y]);
    return neighbors;
  }

  function isWalkable(x, y, h) {
    if (!grid[x] || !grid[x][y]) return false;
    if (visited.has([x, y].join(","))) return false;
    if (!isReverse && getChar(grid[x][y]) <= getChar(h)) return true;
    if (isReverse && getChar(grid[x][y]) >= getChar(h)) return true;
    if (
      Math.abs(getChar(h).charCodeAt(0) - getChar(grid[x][y]).charCodeAt(0)) ===
      1
    )
      return true;
    return false;
  }

  function getChar(c) {
    if (c === "S") return "a";
    if (c === "E") return "z";
    return c;
  }
}