2020 cattle off winter training camp 6 G basic arithmetic sequence brackets

https://ac.nowcoder.com/acm/contest/3007/G
Title Description

Define the legal sequence brackets are:

1. empty sequence is a sequence legitimate brackets

2. If S is a legitimate parenthesis sequence, then (S) is a sequence of legal brackets

3. If A and B are legal brackets sequence, it is a legitimate bracket sequence AB

Now, given a sequence of parentheses, brackets seeking to get at least a few deleting a bracketed sequence legitimate

Input data set comprising T, each set of data, provided in parentheses sequence length N

1≤T,ΣN≤1,000,000

(Since empty string is legitimate bracket sequences, the answer may be N)

Thinking

Simulation of a stack, if they went into the stack, if they are to determine what, if the stack is empty, a record number, if it is left bracket on top of the stack to pop

#include <bits/stdc++.h>
using namespace std;
int T;
const int N = 1e6 + 10;
char s[N];
char st[N];
int top;
int n;
int ans() {
    top = 0;
    int res = 0;
    for (int i = 1; i <= n; i++) {
        if (s[i] == '(') {
            st[++top] = '(';
        }
        else {
            if (top == 0) ++res;
            else if (st[top] == '(') {
                top--;
            }
        }
    }
    res += top;
    return res;
}
int main()
{
    ios::sync_with_stdio(0);
    cin >> T;
    while (T--) {
        cin >> n;
        cin >> s + 1;
        cout << ans() << "\n";
    }
    return 0;
}