driver-less car move

class State {
  int pos;
  int speed;
  String instr;
  State(int p, int s, String str) {
    pos = p; speed = s; instr = str;
  }
  public int hashCode() {
    return pos*31 + speed + 31*31;
  }
  public boolean equals(Object s) {
    if(s == null)
      return false;
    if(!(s instantof State))
      return false;
    State other = (State)s;
    if(this.pos == other.pos)
      return this.speed == other.speed;
    return false;
  }
}

//return the mininum-length instruction seuquences to reach dest from 0
public String mini(int dest) {
  Queue<State> q = new ArrayDeque<>();
  Set<State> visited = new HashSet<>(); //we can use Arrays.toList(state.pos, state.speed) as key as well
  State start = new State(0, 1, "");
  q.offer(start);
  visited.add(start);
  
  while(!q.isEmpty()) {
    Start curr = q.poll();
    if(curr.pos == dest) { //reach the destination
      return curr.instr;
    }
    
   for(State nextState : new State[]{ new State(curr.pos + speed, speed * 2, curr.instr + "A"), 
     new State(curr.pos + speed, speed>0?-1:1, curr.instr + "R") } ) {
      if(!visited.contains(nextState)) {
        visited.add(nextState);
        q.offer(nextState);
      }
    }
  }
  
  return null; //notice this is probably never reached since we will always find a way to reach destination
}