The C++ Set is an associative container that contains a sorted set of unique objects.

**Set Operators**

**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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