Refactor

src/s0009_palindrome_number.cpp

@@ -1,6 +1,6 @@
 #include "s0009_palindrome_number.hpp"
 
-bool Solution::isPalindrome(int x) {
+bool S0009::isPalindrome(int x) {
   string s = to_string(x);
   string r = s;
   reverse(r.begin(), r.end());