<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 generate(int left, int right, string s,vector<string>& answer)
    {
        if (left == 0 && right == 0) {
            answer.push_back(s);
        }
        if (left > right || left < 0 || right < 0) {
            return;
        }
        s.push_back('(');
        generate(left - 1, right, s, answer);
        s.pop_back();

        s.push_back(')');
        generate(left, right - 1, s, answer);
        s.pop_back();
    } 
    vector<string> generateParenthesis(int n) {
        vector<string> ans;
        string s;
        generate(n,n,s,ans);
        return ans;
    }
};
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