56pts不知道错哪，求解

#include <bits/stdc++.h>
using namespace std;

string mb[6] = {"()","[]","(())","([])","()[]","()[()]"};
queue<string> q;
int main(){

    string s,t;
    cin >> s;
    int idx = 0,flag = 0;
    while(1) {

        if(idx >= s.size()) break;
        flag = 0;
        for(int i = 5;i >= 0;i--) {
            if(idx + mb[i].size() > s.size()) continue;
            t = s.substr(idx,mb[i].size());
            if(mb[i] == t) {
                q.push(t);
                flag = 1;
                idx += mb[i].size();
                break;
            }
        }

        if(!flag) {
            if(s[idx] == '(' || s[idx] == ')') {
                q.push("()");
            }else if(s[idx] == '[' || s[idx] == ']') {
                q.push("[]");
            } 

            idx++;  
        }

    }

    while(!q.empty()) {
        cout << q.front();
        q.pop();
    }

    cout << endl;

    return 0;
}