Re: About std::list

"Bo Persson" <>
Sat, 28 Jun 2008 14:03:32 +0200
Jack wrote:

I know I can add/delete items to/from a list at linear time. But
search time thru these lists can be significantly slow. In this
case, should I use a home-brew hash table instead of a list to gain
the benefits of linear time in add/delete and search?
std::vector just won't cut it because it has exponential add/delete
time. Any suggestions?

It also depends on the type of your data. Is it very expensive to
copy? How often do you add and delete elements?

For std::list, complexity of removing an element is actually O(1),
which ignores the constant factor k in k * 1, where k is much larger
than for a std::vector.

The vector isn't exponential either for a single element, it is O(N)
where N is the size of the vector. Here we have the run time k * N,
but with a *much* smaller k.

The performance also depends on the pattern of your deletes. If you
remove the last element of the vector, that is very cheap - much
cheaper than removing the last element of a list. Removing the next to
last element of a vector is just slightly more expensive (one copy of
an element), and so on.

As usual - it depends!

Bo Persson

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