290. Word Pattern

QUESTION:

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.

EXPLANATION:

其实也没有什么特别的，就是一一对应的关系，注意判断是否已经被映射了。

SOLUTION:

public class Solution {
    public boolean wordPattern(String pattern, String str) {
        String[] splits = str.split(" ");
        if(pattern.length()!=splits.length) return false;
        Hashtable<Character,String> reflectTable = new Hashtable<>();
        for(int i = 0;i<pattern.length();i++){
            char key  = pattern.charAt(i);
            Object value = reflectTable.get(key);
            if(value == null){
                String sValue = splits[i];
                boolean containValue = reflectTable.containsValue(sValue);
                if(containValue)//一个新的key，所以他对应的string也应该是单独的，但是如果已经有了，那么就说明已经被映射过了。此时直接return false
                    return false;
                reflectTable.put(key,sValue);
            }else{
                if(!value.equals(splits[i])){
                    return false;
                }
            }
        }
        return true;
    }
}
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