Java [Leetcode 290]Word Pattern

题目描述：

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.

解题思路：

使用HashMap来做。

代码如下：

public class Solution {
    public boolean wordPattern(String pattern, String str) {
    	if(pattern == null || str == null)
    		return false; 
        String[] words = str.split(" ");
        if(pattern.length() != words.length)
        	return false;
        Map<Character, String> map = new HashMap<Character, String>();
        for(int i = 0; i < pattern.length(); i++){
        	char t = pattern.charAt(i);
        	if(map.containsKey(t)){
        		if(!words[i].equals(map.get(t)))
        			return false;
        	} else {
        		if(map.containsValue(words[i]))
        			return false;
        		map.put(t, words[i]);
        	}
        }
        return true;
    }
}