For loop error type mismatch in Scala

Question

i'm learning Scala, but I'm not able go trough the for loop in this code

    def adjacentElementsProduct(inputArray: Array[Int]): Int = {

    var maxSoFar = 0
    var maxHere = 0

    //for (i <- 0:Int to (inputArray.length-1))      <- error
    for (i <- 0 to inputArray.length-1)            //<- error
    {
          if( maxHere * inputArray(i) > 0 )
                maxHere *= inputArray(i)
          else
                maxHere = 0

          if( maxHere > maxSoFar )
                maxSoFar = maxHere

          maxSoFar
    }

}

Compiler results:

(without :Int)

  file.scala on line 6: error: type mismatch;
 found   : Unit
 required: Int
        for (i <- 0 to inputArray.length-1)
               ^

(with :Int)

file.scala on line 6: error: identifier expected but integer literal found.
    for (i <- 0:Int to (inputArray.length - 1) )
                                            ^
file.scala on line 19: error: ')' expected but '}' found.
}
^

What is wrong? How can i solve it?

Thanks a lot, Davide

If maxHere starts at 0, how can maxHere * inputArray(i) ever be > 0? — jwvh
– jwvh, Commented Sep 20, 2017 at 10:19
yeah my fault, i've corrected it with 1 as soon as the for loop worked — Davide Ambrosi
– Davide Ambrosi, Commented Sep 20, 2017 at 10:46

Ziyang Liu · Accepted Answer · 2017-09-20 10:24:09Z

2

adjacentElementsProduct needs to return a Int, you need to put what you want to return at the end of the method (outside the for-loop).

Also you can simplify for (i <- 0 to inputArray.length-1) to for (i <- inputArray) and replace inputArray(i) with i.

edited Sep 20, 2017 at 10:24

answered Sep 20, 2017 at 10:15

Ziyang Liu

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Comments

jwvh · Accepted Answer · 2017-09-20 11:05:39Z

2

If what you're trying to do is return the maximum product of adjacent non-zero integers, here's a more Scala-esque approach.

def adjacentElementsProduct(inputArray: Array[Int]): Int =
  inputArray.scanLeft(0)((a,b) => if (a==0) b else a*b).max

explanation (somewhat simplified)

Think of it this way: myArray.scanLeft(init)(op) will build a new Array that looks something like:

Array( init
     , op(init,             myArray(0))
     , op(previousOpResult, myArray(1))
     , op(previousOpResult, myArray(2))
     . . .
     )

edited Sep 20, 2017 at 11:05

answered Sep 20, 2017 at 10:31

jwvh

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2 Comments

Davide Ambrosi Over a year ago

oh ok, let me understand with that structure it scan the array from 0 to the end i guess, and it create an external temporary structure with all the products so it can find the max value?

jwvh Over a year ago

@DavideAmbrosi; Explanation added.

zhangkuantian · Accepted Answer · 2017-09-20 10:21:48Z

1

the return value maxSoFar should out of the for loop {},like this :

def adjacentElementsProduct(inputArray: Array[Int]): Int = {

    var maxSoFar = 0
    var maxHere = 0

    //for (i <- 0:Int to (inputArray.length-1))      <- error
    for (i <- 0 to inputArray.length-1)            //<- error
    {
          if( maxHere * inputArray(i) > 0 )
                maxHere *= inputArray(i)
          else
                maxHere = 0

          if( maxHere > maxSoFar )
                maxSoFar = maxHere


    }
    maxSoFar

}

answered Sep 20, 2017 at 10:21

zhangkuantian

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