getFirstNonRepeatedLetter

GetFirstNonRepeatedLetter.java

class GetFirstNonRepeatedLetter

	static final int REPEAT = -1;

	public static Character getFirstNonRepeatedLetter(String word) {
		// check if the word is null
		if (word == null) throw new NullPointerException()

		// store a count of character occurrences
		Map<Character, Integer> map = new HashMap<Character, Integer>();
		for (int i = 0; i < word.length(); i++) {
			char c = word.charAt(i)
			// if character exists, mark as REPEAT
			if (map.containsKey(c)) {
				map.put(c, REPEAT);
			} else {
				// put the char and the index of the char
				map.put(c, i);
			}
		}
		int min = Integer.MAX_VALUE;
		Character nonRepeatLetter = null;
		for (Map.Entry<Character, Integer> entry : map.entrySet()) {
			int i = entry.getValue()
			if (i == REPEAT)
				continue;
			// initialize the count
			if (i < min) {
				min = i;
				nonRepeatLetter = entry.getKey();
			}
		}
		return nonRepeatLetter;
	}

}