<p>Given a string <font face="monospace">s</font> of <code>&#39;(&#39;</code> , <code>&#39;)&#39;</code> and lowercase English characters.</p>

<p>Your task is to remove the minimum number of parentheses ( <code>&#39;(&#39;</code> or <code>&#39;)&#39;</code>, in any positions ) so that the resulting <em>parentheses string</em> is valid and return <strong>any</strong> valid string.</p>

<p>Formally, a <em>parentheses string</em> is valid if and only if:</p>

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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;lee(t(c)o)de)&quot;
<strong>Output:</strong> &quot;lee(t(c)o)de&quot;
<strong>Explanation:</strong> &quot;lee(t(co)de)&quot; , &quot;lee(t(c)ode)&quot; would also be accepted.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;a)b(c)d&quot;
<strong>Output:</strong> &quot;ab(c)d&quot;
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;))((&quot;
<strong>Output:</strong> &quot;&quot;
<strong>Explanation:</strong> An empty string is also valid.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s[i]</code> is either&nbsp;<code>&#39;(&#39;</code> , <code>&#39;)&#39;</code>, or lowercase English letter.</li>
</ul>

class Solution {
public:
std::string minRemoveToMakeValid(std::string s) 
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    std::stack<int> openParentheses; // Stack to store indices of '(' characters
    int size = s.size();

    // First pass: Remove invalid ')'
    for(int i = 0; i < size; ++i)
    {
        if(s[i] == '(')
        {
            openParentheses.push(i); // Store the index of the opening parenthesis
        }
        else if(s[i] == ')')
        {
            if(!openParentheses.empty())
            {
                openParentheses.pop(); // Matching opening parenthesis found, pop it from the stack
            }
            else
            {
                s[i] = '*'; // Mark invalid ')' to remove later
            }
        }
    }

    // Second pass: Remove unmatched '('
    while(!openParentheses.empty())
    {
        s[openParentheses.top()] = '*'; // Mark unmatched '(' to remove later
        openParentheses.pop();
    }

    // Remove all marked characters '*'
    s.erase(remove(s.begin(), s.end(), '*'), s.end());

    return s;
}

};
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