MathDebug

SRM 94 · 2002-06-01 · by brett1479

Class Name: MathDebug

Return Type: int

Method Name: getNext

Arg Types: (string)

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.

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

"*"
Returns: 0

"54+6564=465/546=565"
Returns: 3

""
Returns: 1

"123"
Returns: 3

"123+456"
Returns: 5

34)

"1+2="
Returns: 1

Thus far we have which is one valid calculation. We can now accept another valid calculation of the form . Since is next we will only accept a Digit key-press.

35)

"123+"
Returns: 1

Thus far we have so we need the next . The only possible key-press is Digit since if, Equal was given, the second would have a length of 0.

36)

""
Returns: 1

No input has been given thus far so we are waiting for a Digit key-press.

37)

"1"
Returns: 3

The next key-press could be either a Digit or an Operator.

38)

"=123+456="
Returns: 0

The input started with an '=' which is an invalid key-press so the entire computation is invalid.

Submissions are judged against all 42 archived test cases, of which 10 are shown here. Case numbers match the judge’s.

Coding Area

Language: C++17 · define a public class MathDebug with a public method int getNext(string input) · 42 test cases · 2 s / 256 MB per case