242. Valid Anagram

// LeetCode URL: https://leetcode.com/problems/valid-anagram/
import java.util.HashMap;

/**
 * Time Complexity: O(N)
 *
 * Space Complexity: O(N)
 *
 * N = Length of input string S or T.
 */
class Solution {
    public boolean isAnagram(String s, String t) {
        if (s == null || t == null || s.length() != t.length()) {
            return false;
        }
        if (s.length() == 0) {
            return true;
        }

        HashMap<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < s.length(); i++) {
            map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0) + 1);
            map.put(t.charAt(i), map.getOrDefault(t.charAt(i), 0) - 1);
        }

        for (char key : map.keySet()) {
            if (map.get(key) != 0) {
                return false;
            }
        }

        return true;
    }
}