CareerTop Question 1

Data Structures - Arrays and Strings:

Implement an algorithm to determine if a string has all unique characters. What if you can not use additional data structures?

My Original Solution:

        private static boolean uniqueStrByHushTable(String str) {
		boolean flag = false;
		char[] chars = str.toCharArray();
		HashSet<Character> hashSet = new HashSet<Character>();
		for(int i = 0; i < chars.length; i ++) {
			hashSet.add(chars[i]);
		}
		if(hashSet.size()==chars.length) {
			flag = true;
		}
		return flag;
	}

 

Book original solution:

 

	private static boolean uniqueStrByASCII(String str) {
		boolean[] char_val = new boolean[256];
		for (int i = 0; i < str.length(); i++) {
			int val = str.charAt(i);
			if (char_val[val]) {
				return false;
			}
			char_val[val] = true;
		}
		return true;
	}

 

Book original solution 2:

 

private static boolean isUniqueStr(String str) {
		int checker = 0;
		for (int i = 0; i < str.length(); i++) {
			int val = str.charAt(i) - 'a';
			if ((checker & (i << val)) > 0) {
				return false;
			}
			checker |= (1 << val);
		}
		return true;
	}

 

Have no idea about how to check unique string without any data structure.