fix: display lc problem: No.0521 java solution

No.0504.Base 7

Author: YangFong

solution/0500-0599/0504.Base 7/README.md

@@ -43,6 +43,22 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
+class Solution {
+    public String convertToBase7(int num) {
+        if (num == 0) {
+            return "0";
+        }
+        if (num < 0) {
+            return "-" + convertToBase7(-num);
+        }
+        StringBuilder sb = new StringBuilder();
+        while (num != 0) {
+            sb.append(num % 7);
+            num /= 7;
+        }
+        return sb.reverse().toString();
+    }
+}
 
 ```
 

solution/0500-0599/0504.Base 7/README_EN.md

@@ -49,6 +49,22 @@ The input will be in range of [-1e7, 1e7].
 ### **Java**
 
 ```java
+class Solution {
+    public String convertToBase7(int num) {
+        if (num == 0) {
+            return "0";
+        }
+        if (num < 0) {
+            return "-" + convertToBase7(-num);
+        }
+        StringBuilder sb = new StringBuilder();
+        while (num != 0) {
+            sb.append(num % 7);
+            num /= 7;
+        }
+        return sb.reverse().toString();
+    }
+}
 
 ```