<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) {
        vector<string>res;
        backtrack(n,0,0,"",res);
        return res;
    }
private:
    void backtrack(int n,int open,int closed,string curr,vector<string>&res){
        stack<char>st;
        if(open == closed && open == n ){
            res.push_back(curr);
            return ;
        }
        if(open<n){
            backtrack(n, open+1, closed, curr+"(", res);
        }
        if(closed < open){
            backtrack(n,open,closed+1,curr+")",res);
        }   
    }
};

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