[290] Word Pattern

1. 題目描述

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:
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.

給定一個模式和一個使用空格分割的字符串，驗證兩個模式是否相同。

2. 解題思路

首先發現是兩個模式有一個對應關係，如

3. Code

import java.util.HashMap;
import java.util.HashSet;

public class Solution {
    public boolean wordPattern(String pattern, String str) {
        // 分割字符串
        String [] strs = str.split(" ");
        // 兩個模式長度不等，則一定不同
        if (pattern.length() != strs.length)
            return false;
        // 用於存儲pattern[i]到strs[i]的映射關係
        HashMap<String, String> hashMap = new HashMap<>();
        // 用於驗證(a,dog)(b,dog)的情況
        HashSet<String> hashSet = new HashSet<>();
        for (int i = 0; i < pattern.length(); ++i)
        {
            String k = "" + pattern.charAt(i);
            String v = strs[i];
            // 如果key不存在
            if(!hashMap.containsKey(k))
            {
                // 但是set中包含value
                if(hashSet.contains(v))
                    return false;
                // 加入key,value
                hashMap.put(k,v);
                hashSet.add(v);
            }
            else
            {
                // key存在查看對應的值是否相等
                if(!v.equals(hashMap.get(k)))
                {
                    return false;
                }
            }
        }
        return true;
    }
}