Unique-Characters-in-a-String.java

/*
  Implement an algorithm to detemine if a string has all unique characters. 
  What if you cannot use additional data structure.
*/

// solution 1, with an array, time complexity = O(n), space complexity = O(1)
public class  solution  {
    public boolean isUniqueChar(String str) { 
        if(str == null || str.length() == 0)
            return false;
        if(str.length() > 128) return false;
        
        boolean[] char_set = new boolean[256];
        for(int i = 0; i < str.length(); i++) {
            int val = str.charAt(i);
            if(char_set[val])
                return false;
            char_set[val] = true;
        }
        
        return true;
    }
}