Leetcode: 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.

 1 public class Solution {
 2     public boolean wordPattern(String pattern, String str) {
 3         if (pattern==null || str==null) return false;
 4         String[] all = str.split(" ");
 5         
 6         if (pattern.length() != all.length) return false;
 7         HashMap<Character, String> map = new HashMap<Character, String>();
 8         for (int i=0; i<pattern.length(); i++) {
 9             if (!map.containsKey(pattern.charAt(i))) {
10                 if (map.values().contains(all[i])) return false;
11                 map.put(pattern.charAt(i), all[i]);
12             }
13             else {
14                 if (!map.get(pattern.charAt(i)).equals(all[i]))
15                     return false;
16             }
17         }
18         return true;
19     }
20 }