Associative Containers Ordered Unordered Sets Maps as sets of pairs Set API

1. Lecture 10 Associative Containers • Associative Containers • Ordered • Unordered • Sets • Maps as sets of pairs • Set API • Ex: Sieve of Eratosthenes • Implementation • R/B BST • Multisets and Multimaps • Multiset API

2. Associative Containers • Store objects by key • Ordered AC’s • Iterators access elements in key order • Red/black BST implementation • Set, multiset – iterators are const_iterator’s • Map, multimap – half const_iterators? • Stay tuned • Unordered AC’s • Iterators don’t access elements in key order • Hash table implementation • unordered_set, *_multiset – const iters • unordered_map, *_multimap – hybrid like ordered maps

3. Sets set <time24> timeSet;

4. Sets with Key and Satellite Data class Record { T1 key; T2 field1, field2; T3 field3; … public: }; //define lt functor for key // or operator< set <Record> recordSet; pair <set <Record>::iterator, bool> p; p = recordSet.insert (robj); if (! p.second) … … // insert fail?

5. Map: Key-Value Data Map stores data as a key-value pair first component is key (key_type) second is associated value (mapped_type) value_type is pair <const key_type, mapped_type> //<utility> template <typename T1, typename T2> struct std::pair { T1 first; T2 second; // ctor’s };

6. Map Example map <string, int> degreeMajor; // key_type?, value_type? // insert, update?

7. Map Iterator For iterator itr, *itr is of type pair<KeyType, ValueType> Creates complex syntax, so ValueType & operator [ ] (const KeyType & key); If key is present in the map, returns reference to the corresponding value. If not present, it is inserted with a default value and reference is returned.

8. Example Map map<string,double> salaries; salaries[“Pat”] = 75000.00; cout << salaries[“Pat”] << endl; cout << salaries[“Jan”] << endl; map<string,double]::const_iterator itr; itr = salaries.find(“Chris”); if (itr == salaries.end()) cout << “Not an employee.” << endl; else cout << itr->second << endl;

9. Impl: Red/Black Binary Search Tree OAC’s use red-black trees

10. set (); Create an empty set. This is the default constructor. CLASS set CLASS set <set> <set> Constructors Operations set (InputIter first, InputIter last); Initialize the set by using the iterator range [first, last). bool empty () const; Is the set empty? size_t size () const; Return the number of elements in the set.

11. size_t count (const T& key) const; Search for key in the set and return 1 if it is in the set and 0 otherwise. CLASS set <set> Operations iterator find (const T& key); Search for key in the set and return an iterator pointing at it, or end () if it is not found. const_iterator find (const T& key) const; Constant version.

12. CLASS set <set> Operations pair<iterator, bool> insert (const T& key); If key is not in the set, insert it and then return a pair whose first element is an iterator pointing to the new element and whose second element is true. Otherwise, return a pair whose first element is an iterator pointing at the existing element and whose second element is false. Postcondition: The set size increases by 1 if key is not in the set. size_t erase (const T& key); If key is in the set, erase it and return 1; otherwise, return 0. Postcondition: The set size decreases by 1 if key is in the set.

13. void erase (iterator pos); Erase the item pointed to by pos. Preconditions: The set is not empty, and pos points to a valid set element. Postcondition: The set size decreases by 1. CLASS set <set> Operations void erase (iterator first, iterator last); Erase the elements in the range [first, last). Precondition: The set is not empty. Postcondition: The set size decreases by the number of elements in the range.

14. iterator begin (); Return an iterator pointing at the first member in the set. CLASS set <set> Operations const_iterator begin () const; Constant version of begin (). iterator end (); Return an iterator pointing just past the last member in the set. const_iterator end () const; Constant version of end ().

15. Application of Set’s • Sieve of Eratosthenes • STL algorithms that operate on set’s (require ordered ranges) • #include <algorithm> • set_union (In first1, In last1, In first2, In last2, Out res) • set_intersection … • set_difference … • bool includes (In first1, In last1, In first2, In last2)

16. Sieve of Eratosthenes

17. Multisets and Multimaps • Both allow duplicates • insert (…) now returns an iterator, not a pair • Why? • count (key) gives # of occurrences of key • find (key) still used to locate • returns iterator referencing first occurrence • Multimap doesn’t allow operator[]

18. CLASS multiset <set> Operations size_t count (const T& item) const; Return the number of duplicate occurrences of item in the multiset. pair<iterator, iterator> equal_range (const T& item); Return a pair of iterators such that all occurrences of item are in the iterator range [first member of pair, second member of pair). iterator insert (const T& item); Insert item into the multiset and return an iterator pointing at the new element. Postcondition: The element item is added to the multiset.

19. size_t erase (const T& item); Erase all occurrences of item from the multiset and return the number of items erased. Postcondition: Size of multiset is reduced by the number of occurrences of item in the multiset. CLASS multiset <set> Operations