class List
{
  int[] data;
  boolean[] present;
  
  List(int size){
    data = new int[size];
    present = new boolean[size];
    for(int i = 0; i < size; i++){
      data[i] = 0;
      present[i] = false;
    }
  }
  
  void add(int x){
    int i = 0;
    while(present[i] & i < present.length){
      i++;
    }
    if(i == present.length)
      return;
    data[i] = x;
    present[i] = true;
  }
  
  boolean contains(int x){
    for(int i = 0; i < data.length; i++){
      if(data[i] == x & present[i]) 
        return true;
    }
    return false;
  }
  
  void remove(int x){
    for(int i = 0; i < data.length; i++){
      if(data[i] == x & present[i]){ 
        present[i] = false;
        data[i] = 0;
      }
    }
  }
  
  int length(){
    int l = 0;
    for(int i = 0; i < present.length; i++){
      if(present[i])
        l++;
    }
    return l;
  }
  
  public static void main(String args[]){
    List l = new List(100);
    l.add(1);
    l.add(2);
    l.add(3);
    l.remove(2);
    l.add(1);
    l.add(3);
    System.out.println(l.contains(2));
    System.out.println(l.contains(1));
    System.out.println(l.contains(0));
    System.out.println(l.length());
  }
}