Valid combination of parentheses

/**
 * ValidCombinationOfParentheses.java
 * 
 * Description: Implement an algorithm to print all valid (i.e.,
properly opened
 * and closed) combinations of n-pairs of parentheses.
 * 
 * @author John Qiao <qiaoshun8888@gmail.com> Date: Jan 27, 2014
 */