290. 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:

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.

Solution:

There are multiple ways to solve this problem. But the idea is basically the same. 

I will post the most concise one that I saw in the discussion section.

 public boolean wordPattern(String pattern, String str) {  
     String[] words=str.split(" ");  
     HashMap map=new HashMap();  
     if(words.length!=pattern.length()) return false;  
     for(Integer i=0;i<words.length;i++){  
       if(map.put(words[i],i)!=map.put(pattern.charAt(i),i)) return false;  
     }  
     return true;  
   }