Word pattern for leetcode topic analysis

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:

1. pattern = "abba", str = "dog cat cat dog" should return true.
2. pattern = "abba", str = "dog cat cat fish" should return false.
3. pattern = "aaaa", str = "dog cat cat dog" should return false.
4. 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.

Guarantee 1 Yes 1 Mapping

    public boolean wordPattern(String pattern, String str) {
        if (pattern == null || str == null) {
            return false;
        }
        String[] strs = str.split(" ");
        if (pattern.length() != strs.length) {
            return false;
        }
        Map<Character, String> map = new HashMap<Character, String>();
        for (int i = 0; i < pattern.length(); i++) {
            char c = pattern.charAt(i);
            if (map.containsKey(c)) {
                if (!map.get(c).equals(strs[i])) {
                    return false;
                }
            } else {
                //  Guarantee 1 Yes 1 Mapping 
                if (map.containsValue(strs[i])) {
                    return false;
                }
                map.put(c, strs[i]);
            }
        }
        return true;
    }