54场周赛第三题

#include <iostream>
using namespace std;
const int N = 1e6 + 10, inf = 0x3f3f3f3f;
char s[N];
int nums[N];
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, cnt = 0;
    cin >> n;
    cin >> s + 1;
    for(int i = 1; i <= n; i++){
        if(s[i] == '(') cnt++;
    }
    if(abs(n - 2 * cnt) != 2) cout << "0" << endl;
    else{
        for(int i = 1; i <= n; i++){
            if(s[i] =='(') nums[i] = 1;
            else nums[i] = -1;
        }

        int pre = 0, suf = 0, l = n, r = 1;
        for(int i = 1; i <= n; i++){
            pre += nums[i];
            if(pre < 0) {
                l = i - 1;
                break;
            }
        }
        for(int i = n ; i >= 1; i--){
            suf += nums[i];
            if(suf > 0) {
                r = i + 1;
                break;
            }
        }
        int res = 0;
        if(cnt > n - cnt){
            for(int i = r - 1; i <= l; i++)
                if(s[i] =='(') ++res;
        }
        else{
            for(int i = r; i <= l + 1; i++)
                if(s[i] == ')') ++res;
        }
            cout << res << endl;
    }
    return 0;
}