CODEWITHSUNDEEP
kotlinfor-loopmutablelist
Mariano Muendane
Mariano Muendane

Reputation: 13

how to perform dynamic subtraction of a list of numbers with a specific value

My idea is to subtract each value from my list through the value of a variable, for example:

var subtraction = 250
var list = mutableListOf(300, 200, 100)

Then, using the 250 of the subtraction variable, you can dynamically subtract each value of the item, from the last to the first, so with that 250 the program should return: -> list(300, 50). Where 250 is subtracted from item 100 (last item) and then "150" remains from the value "250", and the remaining 150 is subtracted from 200 (second item) and remains 50, thus zeroing out the value of "250" and the program stop. Getting (300, 50) -> 50 which comes from 200 (second item). As if I was going through my list of numbers, subtracting item by item through the value of a variable, from last to first.

Upvotes: -1

Views: 552

Answers (3)

lukas.j
lukas.j

Reputation: 7172

A solution with foldRight using a Pair as accumulator:

val list = listOf(300, 200, 100)
val subtraction = 250

val result = list
  .foldRight(subtraction to emptyList<Int>()) { item, (diff, list) ->
    when {
      diff > item -> diff - item to emptyList()
      else        -> 0           to listOf(item - diff) + list
    }
  }
  .second

println(result)   // Output: [300, 50]

Upvotes: 0

gidds
gidds

Reputation: 18617

The question isn't very clear, but as I understand it: OP wants to modify a list of numbers, subtracting a fixed amount from each, and removing those for which the result would be negative.

If so, it can be done very simply:

list.replaceAll{ it - subtraction }
list.removeIf{ it < 0 }

However, instead of mutating the existing list, it would probably be more common to create a new one:

val newList = list.map{ it - subtraction }.filter{ it >= 0 }

Or, if you need to avoid creating a temporary list:

val newList = list.mapNotNull{ (it - subtraction).takeIf{ it >= 0 } }

Upvotes: 0

Enowneb
Enowneb

Reputation: 1037

Your question still needs further clarification:

  • What should be the output if subtraction = 700?
  • What should be the output if subtraction = 600?
  • What should be the output if subtraction = 100?

The following can be a starting point to solve your question:

fun subtraction() {
  var subtraction = 250
  var list = mutableListOf(300, 200, 100)
  // Loop the list in Reverse order
  for (number in list.indices.reversed()) {
    subtraction -= list[number] // Subtract the last number
    // If subtraction is greater than zero, continue and remove the last element
    if (subtraction > 0)
      list.removeAt(number)
    else {
      // It subtraction is less than or equal to zero, 
      // remove the last element, append the final subtraction result, 
      // and stop the loop
      list.removeAt(number)
      list.add(abs(subtraction))
      break
    }
  }
  // If the subtraction result is still positive after whole list has been processed, 
  // append it back to the list
  // if (subtraction > 0)
  //   list.add(subtraction)
  println(list)
}

Output

[300, 50]

Upvotes: 0

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