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.


    public List<String> findAndReplacePattern(String[] words, String pattern) {
        int[] p = F(pattern);
        List<String> res = new ArrayList<String>();
        for (String w : words)
            if (Arrays.equals(F(w), p)) res.add(w);
        return res;
    }

    public int[] F(String w) {
        HashMap<Character, Integer> m = new HashMap<>();
        int n = w.length();
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            m.putIfAbsent(w.charAt(i), m.size());
            res[i] = m.get(w.charAt(i));
        }
        return res;
    }