1838D - Bracket Walk - CodeForces Solution

#include <set>
#include <iostream>
#include <vector>

using namespace std;


int main() {
    int n, q; cin >> n >> q;
    vector<int> brackets;
    for (int i=0;i<n;i++) {
        char b; cin >> b;
        if (b == '(') brackets.push_back(0);
        else brackets.push_back(1);
    }

    set<int> open_on_odd;
    set<int> closed_on_even;
    for (int i=0;i<n;i++) {
        if (i % 2 == 0 && brackets[i] == 1) closed_on_even.insert(i);
        if (i % 2 == 1 && brackets[i] == 0) open_on_odd.insert(i);
    }

    for (int i=0;i<q;i++) {
        int x; cin >> x;
        x--;
        if (x % 2 == 0){
            if (closed_on_even.find(x) != closed_on_even.end()) {
                closed_on_even.erase(x);
            } else {
                closed_on_even.insert(x);
            }
        } else {
            if (open_on_odd.find(x) != open_on_odd.end()) {
                open_on_odd.erase(x);
            } else {
                open_on_odd.insert(x);
            }
        }

        if (n % 2 != 0) {
            cout << "NO" << endl;
            continue;
        }
        if (open_on_odd.empty() != closed_on_even.empty()) {
            cout << "NO" << endl;
            continue;
        }
        if (open_on_odd.empty() && closed_on_even.empty()) {
            cout << "YES" << endl;
            continue;
        }

        int min_op = *open_on_odd.begin();
        int max_op = *open_on_odd.rbegin();
        int min_cl = *closed_on_even.begin();
        int max_cl = *closed_on_even.rbegin();

        if (min_op < min_cl && max_op < max_cl) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
}