Where Set and Multiset is mostly required

[Rajesh1978]

Hi,
In the Associative container group we have map, multimap, set and multiset.
I can understand why map and multimap is used. But set and multiset makes me think where these containers are useful. We can do the samething by using vector (pushing only unique elements) and sorting them.

so what is the use of Set and multi set??
Thanks

[laserlight]

There is more than one way to skin a cat

[Lindley]

Basically they have different big-Oh costs for some operations. To keep an often-changing vector sorted all the time, you'd have to do a sort on every insertion----O(n*n*log n) in total. A multiset would only require O(n*log n), since it knows how to insert-in-order cheaply unlike a vector. (Even if you explicitly inserted in order, the vector would still need to shuffle over all the greater elements----O(n*n).)

Also, a set is pretty much the easiest way to select a bunch of unique elements if the total number of possible elements is not small. (If it were, you could use a bool array to decide if you'd accepted a given element yet.)