DigitArith

Class Name: DigitArith
Method Name: closestToTarget
Parameters: int, int
Returns: int

Implement a class DigitArith, which contains a method closestToTarget.  The
method takes 2 ints as parameters: a source and a target.  The method performs
3 digit arithmetic operations (defined below) successively on the source and
returns the closest possible result to the target.

Digit Arithmetic Operations:
1. Addition - any digit in the operand can be added to the operand.  Defined
when the result is less than 10,000.
2. Subtraction - any digit in the operand can be subtracted from the operand.
Defined when the result is non-negative.
3. Multiplication - any digit in the operand can be multiplied by the operand.
Defined when the result is less than 10,000.
4. Division - any digit in the operand can divide the operand.  The floor of
the result is taken (Integer Division). Defined when the digit is non-zero.

Note:
-The operations are performed on the result of the previous operation.  ex: for
the second operation, a digit is chosen from the result of the first, not the
source.
-No intermediate results can be negative.
-The digits are always non-negative.

The method signature is:
int closestToTarget(int source, int target);

source and target are non-negative integers less than 1,000.

Example:
-If the source is 12 and the target is 85, the three operations that yeild the
result closest to the target are
 12, take the (2) digit, and multiply: 12*2=24 
 24, take the (4), and multply: 24*4=96 
 96, take the (9), and subtract: 96-9=87
 And the method should return 87.
-If the source is 54 and the target is 13,
 54/4=13 -> 13+1=14 -> 14-1=13.
 And the method should return 13.