1.1 Unique String.java

// 1.1 Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures.

public boolean isUnique(String s){
  int length = s.length();
  // ASCII table only has 128 unique characters, incluing commands
  if(length > 256) return false;
  boolean[] table = new boolean[256];
  for(int i = 0; i < length; i++){
      // Read ASCII int value of character
      int code = (int) s.charAt(i);
      if(!table[code]){
        table[code] = true;
      } else {
        return false;
      }
  }
  // After iterating entire string there's no duplicate characters
  return true;
}