<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:
   string str = "";
    void putParenthesis(vector<string>& res, int open, int close) {
        if(open == 0 && close == 0) {
            res.push_back(str);
            return;
        }
        if(open > 0) {
            str += "(";
            putParenthesis(res, open-1, close);
            str = str.substr(0, str.size()-1);
        }
        if(close > open) {
            str += ")";
            putParenthesis(res, open, close-1);
            str = str.substr(0, str.size()-1);
        }
    }
    vector<string> generateParenthesis(int n) {
        int open = n;
        int close = n;
        vector<string> res;
        putParenthesis(res, open, close);
        return res;
    }
};
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