<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> generateParenthesis(int n) { return helper("", 0, 0, n); }

    vector<string> helper(string curr, int s, int e, int n) {
        if (s == n && e == n)
            return vector<string>{curr};

        vector<string> ans;
        if (s < n)
            for (auto i : helper(curr + "(", s + 1, e, n))
                ans.push_back(i);

        if (e < s)
            for (auto i : helper(curr + ")", s, e + 1, n))
                ans.push_back(i);

        return ans;
    }
};
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