day12-part2.js

const fs = require('fs');

const file = './input.txt';

const input = fs.readFileSync(file, { encoding: 'utf-8'});

const grid = input.split('\n').map(e => e.split(''));

const start = {
  x: -1,
  y: -1,
  effort: 0
}

for (let i = 0; i < grid.length; i++) {
  for (let j = 0; j < grid[i].length; j++) {
    if (grid[i][j] == 'S') {
      start.x = j;
      start.y = i;
      break;
    }
  }
  if (start.x !== -1) {
    break;
  }
}

grid[start.y][start.x] = 'a';

let possibleAStarts = [];

for (let i = 0; i < grid.length; i++) {
  for (let j = 0; j < grid[i].length; j++) {
    if (grid[i][j] == 'a') {
      possibleAStarts.push({
        x: j,
        y: i,
        effort: 0
      });
      break;
    }
  }
}

let possibleMoves = [];

possibleMoves.push(start);

let visitedSquares = [];

const alphabet = 'abcdefghijklmnopqrstuvwxyz';

let effortNeeded = 0;

let possibleAnswers = [];

while (possibleAStarts.length > 0) {
  possibleMoves = [];
  possibleMoves.push(possibleAStarts.pop());
  visitedSquares = [];
  effortNeeded = 0;

  possibleAnswers.push(compute());
}

console.log('ANSWER: ' + possibleAnswers.sort((a, b) => a-b)[0]);

function compute() {
  while (possibleMoves.length > 0) {
    const moveToTry = possibleMoves.shift();
    
    visitedSquares.push(moveToTry);
  
    const squaresToVisit = [
      { x: moveToTry.x - 1, y: moveToTry.y },
      { x: moveToTry.x + 1, y: moveToTry.y },
      { x: moveToTry.x, y: moveToTry.y - 1 },
      { x: moveToTry.x, y: moveToTry.y + 1 }
    ].filter(a => a.x > -1 && a.x < grid[moveToTry.y].length && a.y > -1 && a.y < grid.length);
  
    for (let squareToVisit of squaresToVisit) {
        if (visitedSquares.find(a => a.x === squareToVisit.x && a.y === squareToVisit.y) !== undefined) {
          continue;
        }
        
        if (possibleMoves.find(a => a.x === squareToVisit.x && a.y === squareToVisit.y) !== undefined) {
          continue;
        }
        
        if (grid[squareToVisit.y][squareToVisit.x] === 'E' && 'yz'.indexOf(grid[moveToTry.y][moveToTry.x]) === -1) {
          continue;
        }
        
        if (alphabet.indexOf(grid[squareToVisit.y][squareToVisit.x]) > alphabet.indexOf(grid[moveToTry.y][moveToTry.x]) + 1) {
          continue;
        }
        
        if (grid[squareToVisit.y][squareToVisit.x] === 'E') {
          effortNeeded = moveToTry.effort + 1;
          
          console.log(effortNeeded);
          return effortNeeded;
        }
  
        possibleMoves.push({
          x: squareToVisit.x,
          y: squareToVisit.y,
          effort: moveToTry.effort + 1
        });
    }
  
  }
}