Anagrams O(n)

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Solution {
    static boolean isAnagram(String a, String b) {
        Map<Character, Integer> dictionary = new HashMap<Character, Integer>();
        a = a.toLowerCase();
        b = b.toLowerCase();

        for (int i = 0; i < a.length(); i++) {
            if(!dictionary.containsKey(a.charAt(i))){
                dictionary.put(a.charAt(i), 1);
            } else {
                dictionary.replace(a.charAt(i), dictionary.get(a.charAt(i)) + 1);
            }
        }
        for (int y = 0; y < b.length(); y++) {
            if(!dictionary.containsKey(b.charAt(y))){
                return false;
            } else {
                dictionary.replace(b.charAt(y), dictionary.get(b.charAt(y)) - 1);
            }
        }
        for(Map.Entry<Character, Integer> entry: dictionary.entrySet()){
            if(entry.getValue()!=0){
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String a = scanner.nextLine();
        String b = scanner.nextLine();
        scanner.close();

        System.out.println(isAnagram(a, b)?"Anagrams":"Not Anagrams");
    }
}