anagrams.java

    private static Collection collectAnagrams(String[] dictionary, String searchAnagramsFor) {
        HashMap<Character, Integer> hashMap = new HashMap<>();

        for (int i = 0; i < searchAnagramsFor.length(); i++) {
            char c = Character.toLowerCase(searchAnagramsFor.charAt(i));

            if (!hashMap.containsKey(c)) {
                hashMap.put(c, 0);
            }

            hashMap.put(c, hashMap.get(c) + 1);
        }

        List<String> list = new ArrayList<>();
        for (String el : dictionary) {
            if (el.length() == searchAnagramsFor.length() && isAnagram(el, (HashMap<Character, Integer>) hashMap.clone())) {
                list.add(el);
            }
        }

        return list;
    }

    private static boolean isAnagram(String s1, HashMap<Character, Integer> hashMap) {
        for (int i = 0; i < s1.length(); i++) {
            char c = Character.toLowerCase(s1.charAt(i));

            if (!hashMap.containsKey(c) || hashMap.get(c) == 0) {
                return false;
            }

            hashMap.put(c, hashMap.get(c) - 1);
        }

        return true;
    }