17-Sets_and_Multisets - Associative Containers Data...

Data Retrieval
•
Sequential Container – O(N)
•
Binary Search Tree – O(logN)
SLOW!
How about constant time, O(1) ?
HOW?
Use associative containers (e.g. sets and
maps that allow retrieving elements
by key)!
Associative Containers
Associative Containers

Definition:
Set is an associative container representing a collections of unique
objects.
Example:
{“apples”, “oranges”, “tomatoes”}
Element uniqueness preservation:
{ “apples” , “oranges”, “tomatoes”} + {“apples”} =
{ “apples” , “oranges”, “tomatoes”}
Because “apples” already was in the original set!
Operations:
Union {1, 2, 3} ∪ {4, 5} = {1, 2, 3, 4, 5}
Intersection { 1 , 2, 3 } ∩ { 1 , 3 , 4, 5} = { 1 , 3 }
Subset { 1 , 3 } ⊂ { 1 , 2, 3 } is true
Difference { 1 , 2, 3 } - { 1 , 3 } = {2}
Sets
Sets

#include <set>
set<string> mySet;
size() returns set size;
begin() returns iterator to the first item in the set;
insert(const keyType& item) inserts new element
into the set;
erase(const keyType& item) removes element
from the set;
iterator find(const keyType& item) finds element
in the set (if the item is not found end()
iterator is returned).