<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:
    vector<string> res;
    void generate(string s, int l, int r, int n){
        //cout<<s<<endl;
        if(l<=n)
            generate(s+'(',l+1,r,n);
        if(r<l)
            generate(s+')',l,r+1,n);
        if(l==n && r==n)
            res.push_back(s);
    } 
    vector<string> generateParenthesis(int n) {
        generate("",0,0,n);
        return res;
    }
};
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