Check Balance Binary Tree

**
 * CheckBinaryTreeIsBalance.java
 * 
 * Description: Implement a function to check if a binary tree is
balanced. For
 * the purposes of this question, a balanced tree is defined to be a
tree such
 * that the heights of the two subtrees of any node never differ by more
than
 * one.
 * 
 * @author John Qiao <qiaoshun8888@gmail.com> Date: Jan 23, 2014
 */