<p>Given a string containing just the characters <code>&#39;(&#39;</code> and <code>&#39;)&#39;</code>, return <em>the length of the longest valid (well-formed) parentheses </em><span data-keyword="substring-nonempty"><em>substring</em></span>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;(()&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> The longest valid parentheses substring is &quot;()&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;)()())&quot;
<strong>Output:</strong> 4
<strong>Explanation:</strong> The longest valid parentheses substring is &quot;()()&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;&quot;
<strong>Output:</strong> 0
</pre>

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

<ul>
	<li><code>0 &lt;= s.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>s[i]</code> is <code>&#39;(&#39;</code>, or <code>&#39;)&#39;</code>.</li>
</ul>

class Solution {
public:
    int longestValidParentheses(string s) {
        stack<pair<char,int>> S;

        //Sanitize string
        for(int i =0;i<s.size();i++)
        {
           if(s[i]==')')
           {
            if(!S.empty())
            {
                s[S.top().second]='#',
                s[i]='#';
                S.pop();
            }
           }
           else
           {
              S.push({s[i],i})  ;         
           }
        } 
        cout<<s;
        int Count = 0 ;
        int Max =0;
        for(char ch:s)
        {
            if(ch=='#')
            {
                Count++;
            }
            else
            {
                Count=0;
            }
            Max = max(Count,Max);
        }      
        return Max;
    }
};
10300