290. Word Pattern

Link

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.

Example 1:

Input: pattern = "abba", str = "dog cat cat dog"
Output: true

Example 2:

Input:pattern = "abba", str = "dog cat cat fish"
Output: false

Example 3:

Input: pattern = "aaaa", str = "dog cat cat dog"
Output: false

Example 4:

Input: pattern = "abba", str = "dog dog dog dog"
Output: false

Notes: You may assume pattern contains only lowercase letters, and str contains lowercase letters that may be separated by a single space.

Solution

此題透過Map push function的特性，若之前key值存在就傳回上次的value。的特性來解決。

public boolean wordPattern(String pattern, String str) {
        Map map = new HashMap<>();
        String[] strings = str.split(" ");
        if(strings.length != pattern.length()){
            return false;
        }
        for(int i = 0; i < pattern.length(); i++){
            if(!Objects.equals(
                map.put(strings[i], i), map.put(pattern.charAt(i), i))){
                return false;
            }
        }
        return true;
    }