LeetCode 290. Word Pattern （词语模式）

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.

题目标签：Hash Table

　　题目给了我们一个pattern 和一个 str，让我们判断，str 是否和 pattern 一致。

　　首先，把str split 到 words array 里，如果pattern 的长度和 words 长度不一样，直接返回false；

　　接下来利用HashMap，把pattern 里的 char 当作key，每一个word 当作value 存入，如果遇到一样的char，但是有着不一样的value，返回false；如果遇到不一样的char，但有着一样的value，返回false；最后遍历完之后，返回true。

Java Solution:

Runtime beats 36.87%

完成日期：06/05/2017

关键词：HashMap

关键点：char 当作 key，word 当作 value

 1 class Solution 
 2 {
 3     public boolean wordPattern(String pattern, String str) 
 4     {
 5         HashMap<Character, String> map = new HashMap<>();
 6         
 7         String[] words = str.split(" ");
 8         
 9         if(pattern.length() != words.length)
10             return false;
11         
12         for(int i=0; i<pattern.length(); i++)
13         {
14             char c = pattern.charAt(i);
15 
16             if(map.containsKey(c))
17             {
18                 if(!map.get(c).equals(words[i]))
19                     return false;
20             }
21             else
22             {
23                 if(map.containsValue(words[i]))
24                     return false;
25                 
26                 map.put(c, words[i]);
27             }
28         }
29         
30         return true;
31     }
32 }