Word Pattern

Given a pattern and a string str, find if str follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.

Examples:
pattern = "abba", str = "dog cat cat dog" should return true.
pattern = "abba", str = "dog cat cat fish" should return false.
pattern = "aaaa", str = "dog cat cat dog" should return false.
pattern = "abba", str = "dog dog dog dog" should return false.
Notes:
You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.

    public boolean wordPattern(String pattern, String str) {
        char[] patArr = pattern.toCharArray();
        String[] strArr = str.split(" ");
        if (patArr.length != strArr.length) {
            return false;
        }
        HashMap<Character, String> hm = new HashMap<Character, String>();
        for (int i = 0; i < strArr.length; i++) {
            if (! hm.containsKey(patArr[i])) {
                if (hm.containsValue(strArr[i])) {
                    return false;
                }
                hm.put(patArr[i], strArr[i]);
            } else {
                if (! hm.get(patArr[i]).equals(strArr[i])) {
                    return false;
                }
            }
        }
        return true;
    }