1. insert 'break' after found = true.

2. 

public static boolean isSubsequence(int[] s1, int[] s2)
{
   for (int i = 0; i < s1.length-s2.length+1; i++) {
     boolean match = true;
     for (int j = 0; j < s2.length; j++) {
       if (s1[i+j] != s2[j]) {
         match = false;
         break;
       }
     }
     if (match)
       return true;
   }
   return false;
}

3. 

public class Accounts {
  private Map users = new HashMap();
  
  public static String generatePassword(int min, int max) {
    String s = "";
    int len = min + (int) Math.random()*(max-min);
    for (int i = 0; i < len; i++) {
      char ch = (char) ('a' + (int) (Math.random()*25));
      s += ch;
    }
    return s;
  }
  
  public String register(String userName) {
    String pass = (String) users.get(userName);
    if (pass != null)
      return null;
    pass = generatePassword(4, 10);
    users.put(userName, pass);
    return pass;
  }

  public boolean authentificate(String userName, String password) {
    Object pass = users.get(userName);
    if (pass == null)
      return false;
    return pass.equals(password);
  }
}