Refactor

src/s0020_valid_parentheses.cpp

@@ -1,6 +1,6 @@
 #include "s0020_valid_parentheses.hpp"
 
-bool match(string s1, string s2) {
+bool S0020::match(string s1, string s2) {
   return s1 == "(" && s2 == ")" ||
          s1 == "[" && s2 == "]" ||
          s1 == "{" && s2 == "}";
@@ -8,7 +8,7 @@ bool match(string s1, string s2) {
 
 // 直接用栈
 
-bool Solution::isValid(string s) {
+bool S0020::isValid(string s) {
   stack<string> stack;
   int len = s.length();
   for (int i{0}; i < len; i++) {