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# set vs map in C++ STL

• Difficulty Level : Basic
• Last Updated : 26 May, 2021

set and map in STL are similar in the sense that they both use Red Black Tree (A self balancing BST). Note that the time complexities of search, insert and delete are O(Log n).
Differences
The difference is set is used to store only keys while map is used to store key value pairs. For example consider in the problem of printing sorted distinct elements, we use set as there is value needed for a key. While if we change the problem to print frequencies of distinct sorted elements, we use map. We need map to store array values as key and frequencies as value.

## CPP

 `// CPP program to demonstrate working of set``#include ``using` `namespace` `std;` `int` `main()``{``    ``set<``int``> s1;``    ``s1.insert(2);``    ``s1.insert(5);``    ``s1.insert(3);``    ``s1.insert(6);` `    ``cout << ``"Elements in set:\n"``;``    ``for` `(``auto` `it : s1)``        ``cout << it << ``" "``; ``// Sorted` `    ``return` `0;``}`
Output:
```Elements in set:
2 3 5 6```

## CPP

 `// CPP program to demonstrate working of map``#include ``using` `namespace` `std;` `int` `main()``{``    ``map<``int``, ``int``> m;` `    ``m = 2; ``// Insertion by indexing` `    ``// Direct pair insertion``    ``m.insert({ 4, 5 });` `    ``// Insertion of pair by make_pair``    ``m.insert(make_pair(8, 5));` `    ``cout << ``"Elements in map:\n"``;``    ``for` `(``auto` `it : m)``        ``cout << ``"[ "` `<< it.first << ``", "``             ``<< it.second << ``"]\n"``; ``// Sorted` `    ``return` `0;``}`
Output:
```Elements in map:
[ 1, 2]
[ 4, 5]
[ 8, 5]```

Variations of set and map
Set and Map, both stores unique values and sorted values as well. But If we don’t have such a requirement, we use multiset/multimap and unordered_set/unordered_map.
Multimap: Multimap doesn’t allow elements to stored by indexing.

## CPP

 `// CPP program to demonstrate working of Multimap``#include ``using` `namespace` `std;` `int` `main()``{``    ``multimap<``int``, ``int``> m;` `    ``m.insert({ 1, 2 });``    ``m.insert({ 2, 3 });``    ``m.insert({ 4, 5 });``    ``m.insert({ 2, 3 });``    ``m.insert({ 1, 2 });` `    ``cout << ``"Elements in Multimap:\n"``;``    ``for` `(``auto` `it : m)``        ``cout << ``"[ "` `<< it.first << ``", "``             ``<< it.second << ``"]\n"``; ``// Sorted` `    ``return` `0;``}`
Output:

```Elements in Multimap:
[ 1, 2]
[ 1, 2]
[ 2, 3]
[ 2, 3]
[ 4, 5]```

Multiset

## CPP

 `// CPP program to demonstrate working of Multiset``#include ``using` `namespace` `std;` `int` `main()``{``    ``multiset<``int``> ms;` `    ``ms.insert(1);``    ``ms.insert(3);``    ``ms.insert(4);``    ``ms.insert(2);``    ``ms.insert(2);` `    ``cout << ``"Elements in Multiset:\n"``;``    ``for` `(``auto` `it : ms)``        ``cout << it << ``" "``;` `    ``return` `0;``}`
Output:
```Elements in Multiset:
1 2 2 3 4```

Unordered_set

## CPP

 `// CPP program to demonstrate working of Unordered_set``#include ``using` `namespace` `std;` `int` `main()``{``    ``unordered_set<``int``> us;` `    ``us.insert(1);``    ``us.insert(3);``    ``us.insert(4);``    ``us.insert(2);``    ``us.insert(2);` `    ``cout << ``"Elements in unordered_set:\n"``;``    ``for` `(``auto` `it : us)``        ``cout << it << ``" "``; ``// Sorted` `    ``return` `0;``}`
Output:
```Elements in unordered_set:
2 4 1 3```

Unordered_map

## CPP

 `// CPP program to demonstrate working of Unordered_map``#include ``using` `namespace` `std;` `int` `main()``{``    ``unordered_map<``int``, ``int``> um;` `    ``um = 2;``    ``um = 5;``    ``um = 3;``    ``um = 5;``    ``um = 6;` `    ``cout << ``"Elements in unordered_map:\n"``;``    ``for` `(``auto` `it : um)``        ``cout << ``"[ "` `<< it.first << ``", "` `<< it.second << ``"]\n"``;` `    ``return` `0;``}`
Output:
```Elements in unordered_map:
[ 3, 6]
[ 2, 3]
[ 8, 5]
[ 1, 2]
[ 4, 5]```

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