clearHall.java

public int clearHall() {
    int cnt = 0;
    while (!hallIsClear()) {
        move();
        cnt++; 
    }
    return cnt; 
}

forwardMoveBlocked.java

private boolean forwardMoveBlocked() {
    if (facingRight && pos >= hall.length - 1)
        return true;
    else if (!facingRight && pos == 0)
        return true;
    return false; 
}

move.java

private void move() {
    if (hall[pos] > 0)
        hall[pos]--;
    if (hall[pos] == 0) {
        if (forwardMoveBlocked()) {
            facingRight = !facingRight;
        }
        else if (facingRight) {
            pos++;
        }
        else {
            pos--;
        }
    }
}

Robot.java

public class Robot {
  private int[] hall;
  private int pos; 
  private boolean facingRight;
  
  public boolean forwardMoveBlocked() { // part A }
  private void move() { // part B }
  public int clearHall() { // part C }
  private boolean hallIsClear() {
    // implementation not shown
  }
}