Word Pattern

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题目地址：https://leetcode.com/problems/word-pattern/#/description

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.

题目本身不是很难，将pattern中的每个字母作为key映射到map中，与其对应的str中的word也映射在map中与关联的value的位置，这样只要是map中不存在的key，就直接添加进去，如果存在且value一样，那么继续处理下面的字符，如果value不一样，直接返回false。

但是要考虑到一种情况，pattern=”abba” str=”dog dog dog dog”，这个例子在本题目中是错误的例子，所以要特别注意一下，那么我们如果上面的key和value的位置调换一下，正好就可以处理这种情况了。

最后的结果是上面两种情况的且关系。

下面是代码实现：

public class WordPattern {    public static boolean wordPattern(String pattern, String str) {        if (pattern.length() != str.split(" ").length)            return false;        String[] words = str.split(" ");        boolean posDir = true;        Map<Character, String> posMap = new HashMap<>();        for (int i = 0; i < pattern.length(); i++){            if (!posMap.containsKey(pattern.charAt(i))) {                posMap.put(pattern.charAt(i), words[i]);            } else {                if (posMap.get(pattern.charAt(i)).equals(words[i]))                    continue;                else                    posDir = false;            }        }        boolean negDir = true;        Map<String, Character> negMap = new HashMap<>();        for (int i = 0; i < pattern.length(); i++) {            if (!negMap.containsKey(words[i])) {                negMap.put(words[i], pattern.charAt(i));            }else {                if (negMap.get(words[i]) == pattern.charAt(i))                    continue;                else                    negDir = false;            }        }        return posDir && negDir;    }    public static void main(String[] args) {        System.out.println(wordPattern("abba","dog dog dog dog"));    }}

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