Cfrtjryk

Problem

Given an arithmetic string like 2+2*3 calculate result 8.

Assumptions you can make

• string will be always well formed (no error checking needs to be done)


• only operators passed in string will be + and *


• only single digit numbers allowed

Example

input = 2*2*2+2*1*5

output = 18



input = 2+2*3

output = 8

Hers is scala code for the same

object Expression extends App {

  implicit class Converter(char: Char) {

    def toNum: Int = char - '0'

  }



  def evaluateExpression(s :List[Char]): Int = {

    s match {

      case left::op::List(right) =>  // a+b or a*b

        op match {

          case '+' =>  left.toNum + right.toNum

          case  _ =>   left.toNum * right.toNum

        }

      case left::op::right => // a+b*c or a*b+c

         op match {

           case '+' =>

             left.toNum + evaluateExpression(right)

           case '*' =>

             val nextAdd = right indexOf '+'

             val (multiplication ,pendingExpression) = if (nextAdd == -1) {

                                                         (right,List[Char]())

                                                       } else {

                                                         (right.take(nextAdd), right.drop(nextAdd + 1))

                                                       }

             val product = (multiplication.filter( _ != '*') map (_.toNum)).foldLeft(left.toNum) (_ * _)

             if (pendingExpression.isEmpty) product

             else product + evaluateExpression(pendingExpression)

          }

     }

   }

  List("3*3*3", "2+2*3", "0*0*1", "0+0*1", "0*0*1", "2+2*3*3", "2+2+2*3+2+2") foreach { expr =>

    println(expr + " = " + evaluateExpression(expr.toList))

  }

}

Output for above code

3*3*3 = 27

2+2*3 = 8

0*0*1 = 0

0+0*1 = 0

0*0*1 = 0

2+2*3*3 = 20

2+2+2*3+2+2 = 14

You might want to spend some time becoming more familiar with the Standard Library. You're doing a few things that are already provided for.

implicit class Converter(char: Char) {

  def toNum: Int = char - '0'

}

To convert a digit character into the value it represents: char.asDigit. If you have one or more digit characters in a string: digits.toInt

Your solution also fails for expressions like "2*2+3". It looks like the evaluateExpression() code doesn't anticipate that, in the recursive call evaluateExpression(pendingExpression), the value of pendingExpression might be a single digit.

But mostly, with the input under so many tight restrictions, you should consider what shortcuts might be available to you.

def evaluateExpression(s :String) :Int =

  s.split("\+")

   .map(_.split("\*")

         .map(_.toInt)

         .product)

   .sum