Check unique ASCII chars using bit flags

CrackingTheCode1.java

public class CrackingTheCode1 {
  public static void main(String[] args) {
    CrackingTheCode1 app = new CrackingTheCode1();
    String[] tests = new String[] {
      "abc123", "abc12a", "abc122", "s3cr3t0", "!#%&/()", "#abc123#"
    };
    for (int i = 0; i < tests.length; i++) {
      String s = tests[i];
      System.out.printf("%s : %b\n", s, app.isUniqueChars(s));
    }
  }

  public boolean isUniqueChars(String s) {
    long[] checkers = new long[4];
    int length = s.length();
    for (int i = 0; i < length; i++) {
      int val = s.charAt(i);
      int index = val / 256;
      long offset = (1L << val);

      if ((checkers[index] & offset) > 0) return false;

      checkers[index] |= offset;
    }
    return true;
  }
}