Why is foldRight not giving correct count?-CodePudding

I am trying to calculate the number of elements in a list using foldRight and foldLeft method while foldLeft gives me a correct count foldRight does not. Where am i wrong in the code ?

  def count(arr:List[Int]):Int = {
      arr.foldRight(0)((B,_) => B 1)
    //arr.foldLeft(0)((B,_) => B 1)
  }

val countElements = count(1::2::3::4::Nil)
println(countElements)

The above code returns 2 for foldRight and 4 for foldLeft.

CodePudding user response：

You've swapped the arguments around for foldRight because with fold right the tuple arguments are the other way round, so you are discarding the accumulator and instead adding 1 to the last element (which with foldRight is the first element in the input) so the end result is 2 (the first element 1, plus 1)

If you swap those arguments around i.e.arr.foldRight(0)((_,B) => B 1) you get the expected result of 4