In Scala, how do I fold a List and return the intermediate results?

Question

I\'ve got a List of days in the month:

val days = List(31, 28, 31, ...)

I need to return a List with the cumulative sum of days:

Answer 1

Fold into a list instead of an integer. Use pair (partial list with the accumulated values, accumulator with the last sum) as state in the fold.