#include "s0020_valid_parentheses.hpp"

bool S0020::match(string s1, string s2) {
  return s1 == "(" && s2 == ")" ||
         s1 == "[" && s2 == "]" ||
         s1 == "{" && s2 == "}";
}

// 直接用栈

bool S0020::isValid(string s) {
  stack<string> stack;
  int len = s.length();
  for (int i{0}; i < len; i++) {
    if (stack.empty()) {
      stack.push(s.substr(i, 1));
    } else {
      if (match(stack.top(), s.substr(i, 1))) {
        stack.pop();
      } else {
        stack.push(s.substr(i, 1));
      }
    }
  }
  return stack.empty();
}