Min Stack

/**
 * MinStack.java
 * 
 * Description: How would you design a stack which, in addition to push
and pop,
 * also has a function min which returns the minimum element? Push, pop
and min
 * should all operate in 0(1) time.
 * 
 * @author John Qiao <qiaoshun8888@gmail.com> Date: Jan 23, 2014
 */