The C++ Set is an associative container that contains a sorted set of unique objects.
- begin - returns a reference iterator to the beginning of the set
- clear - deletes all elements from the set
- count - return the number of elements matching a given key
- empty - returns 1 ( true ) if there is no element in the set else return 0 ( false ).
- end - returns a reference iterator just past the last element of a set
- equal_range - returns a reference iterators to the first and just past of the elements matching a specific key.
- erase - deletes elements from a set
- find - returns a reference iterator to specific elements which is given by the user.
- insert - insert an item into a set
- key_comp - returns the function that compares keys
- lower_bound - returns a reference iterator to the first element greater than or equal to a certain value
- max_size - outputs the maximum number of elements that the set can hold
- rbegin - returns a reverse_iterator to the end of the set
- rend - returns a reverse_iterator to the beginning of the set
- size - outputs the number of items in the set
- swap - swap the contents of this set with another set.
- upper_bound - returns a reference iterator to the first element greater than a certain value
- value_comp - returns the function that compares values
Implementation of clear(), empty(), insert(), begin(), end(), count(), lower_bound(), upper_bound()
#include<iostream>
#include<set>
using namespace std;
int main(){
// Create set named si-interger_set.
set<int> si;
// using clear()
si.clear();
cout<<"Is set is empty: "<<si.empty()<<"\n\n";
// insert 5 Element 4,6,7,9,1
si.insert(4);
si.insert(6);
si.insert(7);
si.insert(9);
si.insert(1);
// Printing all element from the set:
cout<<"Printing all the element from the set.\n";
set<int>::iterator iter;
for(iter=si.begin(); iter!=si.end(); iter++){
cout<<*iter<<" ";
}
cout<<"\n\n";
// lower_bound()
cout<<"Lower bound for 3: "<<*(si.lower_bound(3))<<"\n";
// upper_bound()
cout<<"Upper bound for 6: "<<*(si.upper_bound(6))<<"\n\n";
// Counting number of occurances of 7;
cout<<"Occurances of 7 in given set: "<<si.count(7)<<"\n";
return 0;
}
Output:
Is set is empty: 1
Printing all the element from the set.
1 4 6 7 9
Lower bound for 3: 4
Upper bound for 6: 7
Occurances of 7 in given set: 1
begin()
- The begin() returns a reference iterator to the first element of the set.
- begin() runs in constant time O(1).
clear()
- The clear() deletes all of the elements in the set. clear() runs in linear time O(n).
count()
- This count() returns the number of occurrences of a given key value in the set. In a set, it will return 1 if the element is present else 0. In multiset, it will return the occurrences of a given key value in the multiset.
- clear() runs in linear time O(1).
empty()
- The empty() returns true (1) if the set has no elements, false(0) otherwise.
end()
- The end() returns a reference iterator just past the end of the set.
- Note that before you can access the last element of the set using an iterator that you get from a call to end(), you'll have to decrement the iterator first.
equal_range()
- This function returns two reference iterators- one to the first element that contains the key, another to a point just after the last element that contains the key.
erase()
- The erase() either erase the element at the position, erases the elements between start and end or erases all elements that have a value of key.
find()
- The find() function returns a reference iterator to key, or an iterator to the end of the set if the key is not found.
- find() runs in logarithmic time.
Implementation of erase() and find()
#include<iostream>
#include<set>
using namespace std;
int main(){
// Create set named si-interger_set.
set<int> si;
// insert 5 Element 4,6,7,9,1
si.insert(4);
si.insert(6);
si.insert(7);
si.insert(9);
si.insert(1);
// Let's erase the occurance of 6
if(find(si.begin(), si.end(), 6) != si.end()){
si.erase(find(si.begin(), si.end(), 6));
}
for(auto c: si){
cout<<c<<" ";
}
cout<<endl;
return 0;
}
Output:
1 4 7 9
insert()
- The function insert() either:
- inserts value after the element at position (where the position is really just a suggestion as to where the value should go since sets and maps are ordered) and return a reference iterator to that element.
- inserts a range of elements from start to end.
- inserts value, but only if the value doesn't already exist. The return value is an iterator to
- the element inserted, and a boolean describing whether an insertion took place.
key_comp()
- The key_comp() returns the function that compares keys.
- key_comp() runs in constant time O(1).
lower_bound()
- The lower_bound() returns an iterator to the first element which has a value greater than or equal to key.
- lower_bound() runs in logarithmic time O(logn).
max_size()
- The max_size() outputs the maximum number of elements that the set can hold.
- The max_size() should not be confused with the size() or (C++ Strings) capacity().
rbegin()
- The rbegin() function returns a reverse_iterator to the end of the current set.
- rbegin() runs in constant time.
rend()
- The rend() returns a reverse_iterator to the beginning of the current set.
- rend() runs in constant time.
size()
- The size() outputs the number of elements in the current set.
Implementation of size()
#include<iostream>
#include<set>
using namespace std;
int main(){
// Create set named si-interger_set.
set<int> si;
// insert 5 Element 4,6,7,9,1
si.insert(4);
si.insert(6);
si.insert(7);
si.insert(9);
si.insert(1);
cout<<"The size of set: "<<si.size()<<endl;
return 0;
}
Output:
The size of set: 5
swap()
- The swap() function exchanges the elements of the current set with another set.
- This function operates in constant time.
Implementation of swap()
#include <iostream>
#include <set>
using namespace std;
int main() {
// Create set named si-interger_set.
set<int> si1, si2;
// insert 5 Element 4,6,7,9,1
si1.insert(4);
si1.insert(6);
si1.insert(7);
si1.insert(9);
si1.insert(1);
si2.insert(2);
si2.insert(5);
cout<<"Element in si1: ";
for(auto c: si1) cout<<c<<" ";
cout<<endl;
cout<<"Element in si2: ";
for(auto c: si2) cout<<c<<" ";
cout<<endl;
// swapping si1 with si2
si1.swap(si2);
cout<<"Element in after swap si1: ";
for(auto c: si1) cout<<c<<" ";
cout<<endl;
cout<<"Element in after swap si2: ";
for(auto c: si2) cout<<c<<" ";
cout<<endl;
return 0;
}
Output:
Element in si1: 1 4 6 7 9
Element in si2: 2 5
Element in after swap si1: 2 5
Element in after swap si2: 1 4 6 7 9
upper_bound()
- Thi function upper_bound() returns a reference iterator to the first element in the set with a key greater than key.
value_comp()
- The value_comp() returns the function that compares values.
- value_comp() runs in constant time.
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