diff options
Diffstat (limited to 'src/library')
| -rw-r--r-- | src/library/scala/collection/immutable/Stream.scala | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/src/library/scala/collection/immutable/Stream.scala b/src/library/scala/collection/immutable/Stream.scala index 461a375317..78c4d76eda 100644 --- a/src/library/scala/collection/immutable/Stream.scala +++ b/src/library/scala/collection/immutable/Stream.scala @@ -841,9 +841,16 @@ self => * // produces: "1, 2, 3, 4, 5, 6" * }}} */ - override def distinct: Stream[A] = - if (isEmpty) this - else cons(head, tail.filter(head != _).distinct) + override def distinct: Stream[A] = { + // This should use max memory proportional to N, whereas + // recursively calling distinct on the tail is N^2. + def loop(seen: Set[A], rest: Stream[A]): Stream[A] = { + if (rest.isEmpty) rest + else if (seen(rest.head)) loop(seen, rest.tail) + else cons(rest.head, loop(seen + rest.head, rest.tail)) + } + loop(Set(), this) + } /** Returns a new sequence of given length containing the elements of this * sequence followed by zero or more occurrences of given elements. |