Java function that counts the number of unique words in a string, not including punctuation.

CountUniqueWords.java

import java.util.HashMap;

class CountUniqueWords {
    
    /*
     * Given a string, return the number of unique (i.e., non-repeated) words in the string, not including punctuation, in O(n).
     * Hyphenated words such as "case-sensitive" are considered as one word, as are contractions such as "didn't".
     * NOTE: this function is NOT case-sensitive, so "Ball" and "ball" are not considered unique if both are in the string.
     */
    public static int countUniqueWords(String s) {
        HashMap<String, Integer> h = new HashMap<String, Integer>();
        
		String[] words = s.toLowerCase().replaceAll("[^a-zA-Z1-9\\-\\' ]","").split(" ");
		
		//assume every word is unique
		int count = words.length;
		
		//get/put are O(1) in most cases, so this is still O(n)
		for (String word : words) {
			if (h.get(word) == null) {
				h.put(word, 1);
			}
			else {
				h.put(word, (h.get(word) + 1));
			}
		}
		
		int uniqueCount = 0;
		for (String word : words) {
			if (h.get(word) == 1) {
				uniqueCount++;
			}
		}
		return uniqueCount;
	}
    
    
	public static void main(String[] args) {
		String s = "Someone kicked the ball ball Ball Ball-ball";
		System.out.println(CountUniqueWords.countUniqueWords(s));
	}

}