https://school.programmers.co.kr/learn/courses/30/lessons/12909#
#include<string>
#include <iostream>
#include <stack>
using namespace std;
bool solution(string s){
stack <char> st;
for(int i = 0; i < s.size(); i++){
if(s[i] == '(') st.push(s[i]);
else{
if(!st.empty() && st.top() == '(') st.pop();
else st.push(s[i]);
}
}
if(st.empty()) return true;
else return false;
}