## minGap

Author: Whitaker Brand (on 2014/02/13)
```  Write a method called minGap that returns the
minimum gap between adjacent values in a list of integers.  The gap between
two adjacent values in a list is defined as the second value minus the first
value.  For example, suppose a variable called list stores these values:

[1, 3, 6, 7, 12]

The first gap is 2 (3 - 1), the second gap is 3 (6 - 3), the third gap is 1
(7 - 6), and the fourth gap is 5 (12 - 7).  Thus, the call:

list.minGap()

should return 1 because that is the smallest gap.  Notice that the minimum
gap could be a negative number.  For example, if list stores the following:

[3, 5, 11, 4, 8]

The gaps are 2 (5 - 3), 6 (11 - 5), -7 (4 - 11), and 4 (8 - 4).  Of these
values, -7 is the smallest, so it would be returned.

Your method should return 0 if the list has fewer than 2 elements.  You are
writing a method for the LinkedIntList class:

public class ListNode {
public int data;       // data stored in this node
public ListNode next;  // link to next node in the list

<constructors>
}

private ListNode front;

<methods>
}

Your method should not modify the list contents and is required to run in
O(n) time where n is the length of the list.  You may not call any other
methods of the LinkedIntList class and you may not construct any structured
objects to solve this problem.
```

This is a partial class problem. Submit code that will become part of an existing Java class as described. You do not need to write the complete class, just the portion described in the problem.