<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 help(vector<string>& res, string temp,stack<char> st,int open,int close){
        if(!open&&!close){
            res.emplace_back(temp);
            return ;
        }
        if(st.empty()){
            st.emplace('(');
            temp.push_back('(');
            help(res,temp,st,open-1,close);
        }
        else{
            if(open){
                st.emplace('(');
                temp.push_back('(');
                help(res,temp,st,open-1,close);
                st.pop();
                temp.pop_back();
                st.pop();
                temp.push_back(')');
                help(res,temp,st,open,close-1);
            }
            else{
                st.pop();
                temp.push_back(')');
                help(res,temp,st,open,close-1);
            }
        }
        return;
    }
    vector<string> generateParenthesis(int n) {
        vector<string> res;
        stack<char> st;
        help(res,"",st,n,n);
        return res;
    }
};
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