Remove Invalid Parenthesis.cpp

#include <iostream>
#include <queue>
#include <set>
using namespace std;

bool isParenthesis(char c)
{
    return ((c == '(') || (c == ')'));
}

bool isValidString(string str)
{
    int cnt = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str[i] == '(') {
            cnt++;
        } else if (str[i] == ')') {
            cnt--;
        }
        if (cnt < 0) {
            return false;
        }
    }
    return (cnt == 0);
}

void removeInvalidParenthesis(string str)
{
    if (str.empty()) {
        return;
    }
    set<string> visit;
    queue<string> q;
    string temp;
    bool level = false;
    q.push(str);
    visit.insert(str);
    while (!q.empty()) {
        str = q.front();
        q.pop();
        if (isValidString(str)) {
            cout << str << endl;
            level = true;
        }
        if (level) {
            continue;
        }
        for (int i = 0; i < str.length(); i++) {
            if (!isParenthesis(str[i])) {
                continue;
            }
            temp = str.substr(0, i) + str.substr(i + 1);
            if (visit.find(temp) == visit.end()) {
                q.push(temp);
                visit.insert(temp);
            }
        }
    }
}

int main()
{
    cout << "\nEnter Parenthesis\t:\t";
    string expression;
    cin >> expression;
    cout << "\nCorrect Parenthesis\t:\t";
    removeInvalidParenthesis(expression);
    return 0;
}