<p>Given <code>n</code> pairs of parentheses, write a function to <em>generate all combinations of well-formed parentheses</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> n = 3
<strong>Output:</strong> ["((()))","(()())","(())()","()(())","()()()"]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> n = 1
<strong>Output:</strong> ["()"]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 8</code></li>
</ul>

class Solution {
public:
    stack<char> st;
    vector<string>v;
    void valid(int l,int r,int n)
    {
        if(l==n&&r==n)
        {
            stack <char> c=st;
            string w="";
            while(!c.empty())
            {
                w=c.top()+w;
                c.pop();
            }
            v.push_back(w);
        }
    
        if(l<n)
        {
            st.push('(');
            valid(l+1,r,n);
            st.pop();
        }
        if(r<l)
        {
            st.push(')');
            valid(l,r+1,n);
            st.pop();
        }
    }
    vector<string> generateParenthesis(int n) {
        valid(0,0,n);
        return v;
    }
};
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