CC_1_1

UniqueCharacters.java

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

class UniqueCharacters {
	public static boolean hasUniqueCharacters(String s) {

		if (s == null || s.isEmpty()) return true;
		int len = s.length();
		if (len > 256) return false;
		boolean[] hash = new boolean[256];
		for(int i = 0; i < len; i++) {
			char c = s.charAt(i);
			if (hash[c]) {
				return false;
			} else {
				hash[c] = true;
			}
		}
		return true;
	}

	public static void main(String[] args) {
		String test1 = "abc&3";
		String test2 = "fd3j23";
		String test3 = "";
		String test4 = null;
		String test5 = "A";

		assert hasUniqueCharacters(test1);
		assert !hasUniqueCharacters(test2);
		assert hasUniqueCharacters(test3);
		assert hasUniqueCharacters(test4);
		assert hasUniqueCharacters(test5);

		System.out.println("Test Passed");
	}
}

if (len > 256) return false; good catch