(String). 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
   

   public class Solution {       //if不用hashmap，更好的方法是设置头尾“指针”，保证一个指向当前的值
       public boolean wordPattern(String pattern, String str) {
       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++) {
   			if (map.containsKey(pattern.charAt(i))
   					&& !(map.get(pattern.charAt(i))).equals(strs[i]))
   				return false;
   			if (!map.containsKey(pattern.charAt(i))
   					&& map.containsValue(strs[i]))
   				return false;
   			if (!map.containsKey(pattern.charAt(i))
   					&& !map.containsValue(strs[i]))
   				map.put(pattern.charAt(i), strs[i]);
   		}
   		return true;
       }
   }