MathDebug | Topcoder Archive

Problem Statement

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.

Definition

Class:: MathDebug
Method:: getNext
Parameters:: String
Returns:: int
Method signature:: int getNext(String input)
(be sure your method is public)

Constraints

input will only contain characters within the following string: "0123456789+-*/=" (quotes are for clarity).
input will have length between 0 and 50 characters, inclusive.

Examples

```
"1+2="
```
```
Returns: 1
```
Thus far we have <NUMBER><OPERATOR><NUMBER><EQUALS> which is one valid calculation. We can now accept another valid calculation of the form <NUMBER><OPERATOR><NUMBER><EQUALS>. Since <NUMBER> is next we will only accept a Digit key-press.
```
"123+"
```
```
Returns: 1
```
Thus far we have <NUMBER><OPERATOR> so we need the next <NUMBER>. The only possible key-press is Digit since if, Equal was given, the second <NUMBER> would have a length of 0.
```
""
```
```
Returns: 1
```
No input has been given thus far so we are waiting for a Digit key-press.
```
"1"
```
```
Returns: 3
```
The next key-press could be either a Digit or an Operator.
```
"=123+456="
```
```
Returns: 0
```
The input started with an '=' which is an invalid key-press so the entire computation is invalid.
```
"1234+123=98*0"
```
```
Returns: 5
```
```
"98+01234=234*1230=000/000="
```
```
Returns: 1
```
```
"98+76+23="
```
```
Returns: 0
```

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