add leetcode problem-cn part2

算法题（国内版）/problem (English)/括号(English) [bracket-lcci].html

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+<p>Implement an algorithm to print all valid (e.g., properly opened and closed) combinations of n pairs of parentheses.</p>
+
+<p>Note: The result set should not contain duplicated subsets.</p>
+
+<p>For example, given&nbsp;n = 3, the result should be:</p>
+
+<pre>
+[
+  &quot;((()))&quot;,
+  &quot;(()())&quot;,
+  &quot;(())()&quot;,
+  &quot;()(())&quot;,
+  &quot;()()()&quot;
+]
+</pre>