<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) {
        if(n==1){
            return {"()"};
        }

        unordered_set<string> st;
        vector<string> tmp = generateParenthesis(n-1);
        vector<string> ans;

        for(auto s: tmp){
            for(int i=0;i<=s.size();i++){
                string s1 = s.substr(0,i);
                string s2 = s.substr(i);
                st.insert(s1+"()"+s2);
            }
        }        

        for(auto z:st){
            ans.push_back(z);
        }

        return ans;
    }
};
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