学校信息课 python 的水题，我用 c++ 做结果 MLE 了

#include <bits/stdc++.h>
using namespace std;
string s;
bool a,b,c;
bool check(char ch)
{
    if ('1' <= ch && ch <= '9')
        a = 1;
    else if ('a' <= ch && ch <= 'z')
        b = 1;
    else if ('A' <= ch && ch <= 'Z')
        c = 1;
}
int main()
{
    cin >> s;
    if (s.length() < 6)
    {
        cout << "不符合要求" << endl;
        return 0;
    }
    for (int i = 0;i < s.length();i++)
        check(s[i]);
    if (a && b && c)
        cout << "符合要求" << endl;
    else
        cout << "不符合要求" << endl;
    return 0;
}