LeetCode - Word Patttern

WordPattern.java

// 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) {
    if(pattern == null || pattern.length() == 0) return pattern.equals(str);
    String[] strCollection = str.split(" ");
    if(strCollection.length != pattern.length()) return false;
    HashMap<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(strCollection[i])) return false;
        } else{
            if(map.containsValue(strCollection[i])) return false;
            map.put(c, strCollection[i]);
        }
    }
    return true;
}