Map定义层级和存储括号对，stack出入匹配括号

#include <iostream>
#include <stack>
#include <map>
#include <string>
using namespace std;

int main() {
    int n;
    cin >> n;
    string line;
    getline(cin, line); // consume the newline after n

    // 定义括号层级：越小越外层
    map<char, int> level;
    level['{'] = 0;
    level['['] = 1;
    level['('] = 2;
    level['<'] = 3;

    // 右括号到左括号的映射
    map<char, char> match;
    match['}'] = '{';
    match[']'] = '[';
    match[')'] = '(';
    match['>'] = '<';

    for (int idx = 0; idx < n; ++idx) {
        getline(cin, line);
        stack<char> st;
  ...