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.

思路：题目要求保持一一对应的关系，那就用两个hashmap保存住一一对应关系，然后每次循环检测是否对应即可。否则return false

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