<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;
    vector<string> generateParenthesis(int n) {
        gen(n*2, 0, "");
        return res;
    }

    void gen (int n, int open, string curr){
        if (n==0 && open==0){
            res.push_back(curr);
        }
        if (n<0){
            return;
        }
        gen(n-1, open+1, curr+"(");
        if (open>0){
            gen(n-1, open-1, curr+")");
        }
    }
};


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