diff --git a/problems/0242.有效的字母异位词.md b/problems/0242.有效的字母异位词.md
index 87302482..d54285eb 100644
--- a/problems/0242.有效的字母异位词.md
+++ b/problems/0242.有效的字母异位词.md
@@ -92,18 +92,24 @@ public:
 
 Java：
 ```java
+/**
+ * 242. 有效的字母异位词 字典解法
+ * 时间复杂度O(m+n) 空间复杂度O(1)
+ */
 class Solution {
     public boolean isAnagram(String s, String t) {
-
         int[] record = new int[26];
-        for (char c : s.toCharArray()) {
-            record[c - 'a'] += 1;
+
+        for (int i = 0; i < s.length(); i++) {
+            record[s.charAt(i) - 'a']++;
         }
-        for (char c : t.toCharArray()) {
-            record[c - 'a'] -= 1;
+
+        for (int i = 0; i < t.length(); i++) {
+            record[t.charAt(i) - 'a']--;
         }
-        for (int i : record) {
-            if (i != 0) {
+        
+        for (int count: record) {
+            if (count != 0) {
                 return false;
             }
         }