Scala 中的运行总和流 [英] Stream of running sums in Scala

问题描述

这是我上一个问题的后续.
给定函数 add_stream(s1:Stream[Int], s2:Stream[Int]):Stream[Int]我想编码 running_sums(s:Stream[Int]):Stream[Int]，它返回一个新的流:s1, s1 + s2, s1 + s2 + s3, ...

This is a follow-up to my previous question.
Given function add_stream(s1:Stream[Int], s2:Stream[Int]):Stream[Int] I would like to code running_sums(s:Stream[Int]):Stream[Int], which returns a new stream : s1, s1 + s2, s1 + s2 + s3, ...

我可以想到以下实现，但如果 s 为空，则它不起作用

I can think of the following implementation but it does not work if s is empty

def running_sums(s:Stream[Int]):Stream[Int] =
  Stream.cons(s.head, add_streams(s.tail, running_sums(s)))

我可以按如下方式修复它:

I can fix it as follows:

def running_sums(s:Stream[Int]):Stream[Int] =
  if (s.isEmpty) empty
    else Stream.cons(s.head, add_streams(s.tail, running_sums(s)))

但是它看起来并不优雅.

However it does not look elegant.

您将如何实现 running_sums?

推荐答案

有一个类似这样的库调用，叫做 scanLeft

There's a library call for something like this, called scanLeft

s.scanLeft(0)(_+_).tail

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