Statistics

You are writing the embedded software to make sure a calculator functions properly. This is a special calculator that allows simple arithmetic with very large integers. The following rules are in place for PROPER USAGE (quotes used for clarity):

1) A valid calculation consists of <NUMBER><OPERATOR><NUMBER><EQUALS> where:

• <NUMBER> is a string of one or more digits('0'..'9')
• <OPERATOR> is one of '+','-','*','/'
• <EQUALS> is '='

2) The calculator can perform a sequence of valid calculations in a row.

• So 98+01234=234*1230=000/000= is valid where
• 98+01234= is the first calculation,
• 234*1230= is the second and
• 000/000= is the last.

Embedded logic is needed to determine what the next key-press should be. Your function will return what key-press the calculator can accept next according to the following schema (quotes used for clarity):

Next key-press                                : Return
--------------------------------------------------------
Digit ('0'..'9')                             : 1
Operator ('+','-','*','/')                   : 2
Digit or Operator ('0'..'9','+','-','*','/') : 3
Equals ('=')                                 : 4
Digit or Equals ('0'..'9','=')               : 5

For example, if you have:
"47"
The next key-press could either be a Digit or an Operator so you would return 3.

If the input given doesn't follow the above laws of PROPER USAGE you should return 0. This means that invalid key-presses occurred previously and your calculator is no longer in a functioning state. For example, if you have:
"53++6=12+"
The input has 2 consecutive Operator key-presses("++") so the entire input violates PROPER USAGE and you will return 0.

Create a class MathDebug that contains the method getNext, which takes a String, input, and returns an int that represents valid next key-presses or 0 if there is an error in the input.