[
https://issues.apache.org/jira/browse/CALCITE-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17134400#comment-17134400
]
Julian Hyde commented on CALCITE-4049:
--------------------------------------
You don't seem to realize that it is a trade-off. A change that improves some
things makes other things worse. It is glib of you to say 'computers have more
memory now, so there's no trade-off'.
Cons is a general-purpose data structure. You made it better for your purposes
but you have not considered other purposes.
The best practice with data structures is to be explicit about the cost for
various operations. In Cons, the running time of size is O(n). People
understand and accept that.
> Reduce the time complexity of getting shortest distances
> --------------------------------------------------------
>
> Key: CALCITE-4049
> URL: https://issues.apache.org/jira/browse/CALCITE-4049
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Fix For: 1.24.0
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> Currently, we have {{Graphs#makeImmutable}} to compute the shortest paths
> between all pairs of nodes. For many scenarios, however, we do not need the
> exact paths between nodes. Instead, we are only interested in the lengths of
> the shortest paths.
> To get the path length, we need to get the shortest path first, which is
> returned as a {{List}}, then we call the {{List#size()}} method. According to
> the current implementation, the returned list is of type {{ConsList}}. The
> time complexity of {{ConsList#size}} is O(p) (p is the number of vertices on
> the path), which is inefficient.
> In this issue, we revise the implementation of {{ConsList#size}} so that it
> takes O(1) time. In addition, we also give a utiltiy to get the shortest
> distances between nodes.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
