# Min Remove Parentheses

````cpp
// https://leetcode.com/problems/minimum-remove-to-make-valid-parentheses/

/*
Given a string s of '(' , ')' and lowercase English characters.

Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid and return any valid string.

Formally, a parentheses string is valid if and only if:

It is the empty string, contains only lowercase characters, or
It can be written as AB (A concatenated with B), where A and B are valid strings, or
It can be written as (A), where A is a valid string.

Ex1:
Input: s = "lee(t(c)o)de)"
Output: "lee(t(c)o)de"
Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.

Ex2:
Input: s = "a)b(c)d"
Output: "ab(c)d"

Ex3:
Input: s = "))(("
Output: ""
Explanation: An empty string is also valid.
*/

#include <string>
#include <stack>
#include <iostream>

using namespace std;

string minRemoveToMakeValid(string s) {
    if (s.empty()) {
        return "";
    }

    stack<int> st;
    int n = s.size();
    for (int i = 0; i < n; i++) {
        if (s[i] == '(') {
            st.push(i);
        } else if (s[i] == ')') {
            if (!st.empty() && s[st.top()] == '(') {
                st.pop();
            } else {
                st.push(i);
            }
        }
    }

    string res;
    for (int i = n-1; i >= 0; i--) {
        if (!st.empty() && i == st.top()) {
            st.pop();
            continue;
        }
        res.push_back(s[i]);
    }

    reverse(res.begin(), res.end());
    return res;
}

string minRemoveToMakeValidWithoutStack(string s) {
    string res;
    int left = 0, right = 0;
    for (char c : s) {
        if (c == ')') ++right;
    }
    for (char c : s) {
        if (c == '(') {
            if (left == right) continue;
            ++left;
        }
        else if (c == ')') {
            --right;
            if (left == 0) continue;
            --left;
        }
        res += c;
    }
    return res;
}

int main() {
    cout << minRemoveToMakeValid("lee(t(c)o)de)") << endl;
    cout << minRemoveToMakeValid("a)b(c)d") << endl;
    cout << minRemoveToMakeValid("))((") << endl;

    return 0;
}```
````


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://dongzeli95s-organization.gitbook.io/swe-interview-handbook/algorithm/stack/min_remove_parentheses.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.