String - 290. Word Pattern

class Solution {

    public boolean wordPattern(String pattern, String str) {
        if (pattern == null || str == null) return true;
        
        String[] strs = str.split(" ");
        if (strs.length != pattern.length()) return false;
        
        Map index = new HashMap();
        for (Integer i = 0; i < strs.length; i++) {
            if (index.put(pattern.charAt(i), i) != index.put(strs[i], i)) // return null or old value
                return false;
        }
        
        return true;
    }
}