<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 {
    vector<string> ans;
    void solve(string s, int cnt, int open) {
        if (cnt == 0) {
            if (open == 0)
                ans.push_back(s);
            return;
        }
        if (open > 0) {
            s += ')';
            solve(s, cnt - 1, open - 1);
            s.pop_back();
        }
        s += '(';
        solve(s, cnt - 1, open + 1);
        s.pop_back();
    }

public:
    vector<string> generateParenthesis(int n) {
        solve("", 2 * n, 0);
        return ans;
    }
};
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