96 lines
3.2 KiB
Markdown
96 lines
3.2 KiB
Markdown
---
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title: Set
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---
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A set data structure in c++ is defined the same way a set is defined in the context of mathematics.
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More formally speaking, Sets are a type of associative containers in which each element has to be unique.
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* The value of the element cannot be modified once it is entered, although deleting an element and inserting a new element is allowed, the same way we do in mathenatics.
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* Set data sructure can be used to model, well, sets itself. It becomes easy to find intersections, unions etc.
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* Similar to vector, but only unique values are allowed.
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* Set arranges the elements in increasing order as and when you insert elements into the set.
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The header file required for using the set data structure is 'set'. i.e, `#include<set>` must be there in your code for you to use the set data structure.
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__Pro tip__:- Use `#include<bits/stdc++.h>` to include all C++ data structures and functions, instead of adding them one by one.
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<br>
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Some of the functions that can be performed with a set:-
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1. begin() – Returns an iterator to the first element in the set
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1. end() – Returns an iterator to the theoretical element that follows last element in the set
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1. size() – Returns the number of elements in the set
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1. max_size() – Returns the maximum number of elements that the set can hold
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1. empty() – Returns whether the set is empty
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1. erase(const g)- Removes the value ‘g’ from the set
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1. clear() – Removes all the elements from the set
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Let us look at an example :-
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```cpp
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#include <iostream>
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#include <set>
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#include <iterator>
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using namespace std;
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int main()
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{
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set <int> myset; //an empty set container. Note that size of the set need not be declared, similar to vector.
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// insert elements in random order
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myset.insert(65);
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myset.insert(30);
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myset.insert(80);
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myset.insert(20);
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myset.insert(9);
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myset.insert(9); // only one 9 will be added to the list.
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// printing set myset
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set <int> :: iterator itr; //an iterator is like a pointer.
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cout << "\nThe contents of myset : ";
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for (itr = myset.begin(); itr != myset.end(); ++itr)
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{
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cout << '\t' << *itr;
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}
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cout << endl;
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// remove all elements up to 65 in myset from the beginning:-
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cout << "\nContents of myset after removal of elements less than 30 : ";
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myset.erase(myset.begin(), myset.find(30));
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for (itr = myset.begin(); itr != myset.end(); ++itr)
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{
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cout << '\t' << *itr;
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}
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// remove element with value 50 in myset
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int num = myset.erase(80); //returns true (and deletes) if 80 is there in the list else returns 0.
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cout<<"\n\n After doing myset.erase(80), "<<num<<" element is removed\n\n";
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cout<<"Contents of the modified set:\t";
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for (itr = myset.begin(); itr != myset.end(); ++itr)
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{
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cout << '\t' << *itr;
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}
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cout << endl;
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return 0;
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}
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```
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```cpp
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Output:-
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The contents of myset : 9 20 30 65 80
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Contents of myset after removal of elements less than 30 : 30 65 80
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After doing myset.erase(80), 1 element is removed
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Contents of the modified set: 30 65
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```
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### Sources
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1. [Geeks for Geeks](https://www.geeksforgeeks.org/set-in-cpp-stl/)
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