<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:

 void helper(string str,int cnt,int n,vector<string> &ans){
        if(str.size() == n*2){

            if(cnt==0) ans.push_back(str);
            return;

        }

        if(cnt>=0 && cnt<n){
            helper(str+'(',cnt+1,n, ans);
        }
            
        if(cnt<=n && cnt>0){
            helper(str+')',cnt-1,n, ans);
        }
    }
    vector<string> generateParenthesis(int n) {
        vector<string> ans;
        string str;
        helper(str, 0, n, ans);
        return ans;
    }
};
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