Find magic index 

/**
 * FindMagicIndexInArray.java
 * 
 * Description: AmagicindexinanarrayA[l...n-l] is defined to be an index
such
 * that A[i] = i. Given a sorted array of distinct integers, write a
method to
 * find a magic index, if one exists, in array A. 
 * 
 * FOLLOW UP What if the values are not distinct?
 * 
 * @author John Qiao <qiaoshun8888@gmail.com> Date: Jan 27, 2014
 */