[Java 101] 242. Valid Anagram with HashMap

class Solution {
    public boolean isAnagram(String s, String t) {
        if (s.length() != t.length())
            return false;

        Map<Character, Integer> counter1 = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            counter1.merge(c, 1, Integer::sum);
        }
        Map<Character, Integer> counter2 = new HashMap<>();
        for (int i = 0; i < t.length(); i++) {
            char c = t.charAt(i);
            counter2.merge(c, 1, Integer::sum);
        }

        for (Character c : counter1.keySet()) {
            if (!counter1.get(c).equals(counter2.get(c)))
                return false;
        }
        return true;
    }
}