The-Bridge.js

// https://www.codingame.com/training/hard/the-bridge-episode-2
// M - the amount of motorbikes to control
// V -  the minimum amount of motorbikes that must survive

const [M, V] = [+readline(), +readline()];
const roads = Array(4)
  .fill()
  .map(_ => readline().split``.map(c => c === '.'));
const roadLength = roads[0].length;
const copy = bikes => bikes.map(b => ({ x: b.x, y: b.y, speed: b.speed }));

const findPath = (original, V) => {
  const results = [];
  const applyMove = (bikes, move) =>
    bikes
      .map(bike => {
        const next = bike.x + bike.speed;
        let nextLane = bike.y;
        let checked = roads[bike.y].slice(bike.x, next);

        if (move === 'UP' || move === 'DOWN') {
          if (
            (move === 'UP' && bike.y === 0) ||
            (move === 'DOWN' && bike.y === 3)
          ) {
            checked = [];
            bikes = [];
          } else {
            nextLane = bike.y + (move === 'UP' ? -1 : 1);
            checked.push(...roads[nextLane].slice(bike.x, next));
          }
        }
        if (
          (checked.some(x => !x) && move !== 'JUMP') ||
          (next < roadLength && !roads[nextLane][next])
        ) {
          return null;
        }
        [bike.x, bike.y] = [next, nextLane];

        return bike;
      })
      .filter(b => b);

  for (let move of ['SPEED', 'WAIT', 'JUMP', 'DOWN', 'UP', 'SLOW']) {
    let bikes = copy(original);

    if (move === 'SPEED') {
      bikes.forEach(b => b.speed++);
    } else if (move === 'SLOW') {
      bikes.forEach(b => b.speed--);
      if (bikes[0].speed === 0) {
        bikes = [];
      }
    }

    bikes = applyMove(bikes, move);
    bikes.length >= V && results.push({ move: move, bikes: bikes });
  }

  return results;
};

const backtrack = (bikes, V) => {
  const [stack, moves] = [[bikes], []];

  while (stack.length) {
    bikes = stack[0];
    !bikes.next && ((bikes.next = findPath(bikes, V)), (bikes.id = 0));

    if (bikes[0].x >= roadLength) {
      return moves.reverse();
    }

    if (bikes.id < bikes.next.length) {
      let next = bikes.next[bikes.id++];
      stack.unshift(next.bikes);
      moves.unshift(next.move);
    } else {
      stack.shift();
      moves.shift();
    }
  }
  return null;
};

let move = null;

// game loop
while (true) {
  const [speed, bikes] = [+readline(), []];

  for (let i = 0; i < M; i++) {
    let [x, y, active] = readline().split` `.map(n => +n);
    active && bikes.push({ x, y, speed });
  }

  for (let expected = bikes.length; !move && expected >= V; expected--) {
    move = backtrack(copy(bikes), expected);
  }

  print(move.shift() || 'WAIT');
}