<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) {
        set<string>ans;
        ans.insert("()");

        for(int i=2; i<=n; i++)
        {
            set<string>next;
            for(auto &it:ans)
            {
                for(int j=1; j<=it.size(); j++)
                {
                    string newStr = it.substr(0, j) + "()" + it.substr(j);
                    next.insert(newStr);
                }
            }
            ans = next;
        }

        return vector<string>(ans.begin(), ans.end());
    }
};
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