890. Find and Replace Pattern

890. Find and Replace Pattern

You have a list of words and a pattern, and you want to know which words in words matches the pattern.

A word matches the pattern if there exists a permutation of letters p so that after replacing every letter x in the pattern with p(x), we get the desired word.

(Recall that a permutation of letters is a bijection from letters to letters: every letter maps to another letter, and no two letters map to the same letter.)

Return a list of the words in words that match the given pattern. 

You may return the answer in any order.

Example 1:

Input: words = ["abc","deq","mee","aqq","dkd","ccc"], pattern = "abb"
Output: ["mee","aqq"]
Explanation: "mee" matches the pattern because there is a permutation {a -> m, b -> e, ...}. 
"ccc" does not match the pattern because {a -> c, b -> c, ...} is not a permutation,
since a and b map to the same letter.

Note:

• 1 <= words.length <= 50
• 1 <= pattern.length = words[i].length <= 20

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class Solution {
    public List findAndReplacePattern(String[] words, String pattern) {
        List rt = new ArrayList<>();
        for (String w : words) {
            if (helper(w, pattern)) {
                rt.add(w);
            }
        }
        
        return rt;
    }
    
    private boolean helper(String word, String p) {
        Map map = new HashMap<>();
        Set used = new HashSet<>();
        
        for (int i = 0; i < p.length(); i++) {
            char pc = p.charAt(i);
            char c = word.charAt(i);
            if (map.containsKey(pc) && map.get(pc) != c) return false;
            if (!map.containsKey(pc) && used.contains(c)) return false;
            
            map.put(pc, c);
            used.add(c);
        }
        
        return true;
    }
}