<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;
    void allcomb(int opn,int cls,string s,int n){
        if(cls==0){
            ans.push_back(s);
            return;
        }
        if(opn<cls){
            if(opn!=0){
                s[n]='(';
                allcomb(opn-1,cls,s,n+1);
            }
            s[n]=')';
            allcomb(opn,cls-1,s,n+1);
        }
        else{
            s[n]='(';
            allcomb(opn-1,cls,s,n+1);
        }

    } 
    vector<string> generateParenthesis(int n) {
        string s(2*n,' ');
        allcomb(n,n,s,0);
        return ans;   
    }
};
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