<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>ans;
    unordered_set<string>vis;
    void generate(int n,int l,int r,string x){
        // cout<<x<<' '<<l<<' '<<r<<'\n';
        if(vis.find(x)==vis.end()){
            vis.insert(x);
            if(l>n or r>n) return;
            if(l==r and l==n) ans.push_back(x);
            generate(n,l+1,r,x+"(");
            if(l>r) generate(n,l,r+1,x+")");
        }
    }
    vector<string> generateParenthesis(int n) {
        generate(n,0,0,"");
        return ans;
    }
};
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