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Dominant Set of a Graph
• Last Updated : 04 Feb, 2020

In graph theory, a dominating set for a graph G = (V, E) is a subset D of V such that every vertex not in D is adjacent to at least one member of D. The domination number is the number of vertices in a smallest dominating set for G. Examples:

```Input :   A graph with 4 vertex and 4 edges Output :  The Dominant Set S= { a, b } or { a, d } or { a, c } and more.

Input : A graph with 6 vertex and 7 edges Output :  The Dominant Set S= { a, d, f } or { e, c } and more.
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

It is believed that there may be no efficient algorithm that finds a smallest dominating set for all graphs, but there are efficient approximation algorithms.
Algorithm :

• First we have to initialize a set ‘S’ as empty
• Take any edge ‘e’ of the graph connecting the vertices ( say A and B )
• Add one vertex between A and B ( let say A ) to our set S
• Delete all the edges in the graph connected to A
• Go back to step 2 and repeat, if some edge is still left in the graph
• The final set S is a Dominant Set of the graph

## C++

 `// C++ program to find the Dominant Set of a graph``#include ``using` `namespace` `std;`` ` `vector > g;``bool` `box;`` ` `vector<``int``> Dominant(``int` `ver, ``int` `edge)``{``    ``vector<``int``> S; ``// set S``    ``for` `(``int` `i = 0; i < ver; i++) {``        ``if` `(!box[i]) {``            ``S.push_back(i);``            ``box[i] = ``true``;``            ``for` `(``int` `j = 0; j < (``int``)g[i].size(); j++) {``                ``if` `(!box[g[i][j]]) {``                    ``box[g[i][j]] = ``true``;``                    ``break``;``                ``}``            ``}``        ``}``    ``}``    ``return` `S;``}`` ` `// Driver function``int` `main()``{``    ``int` `ver, edge, x, y;`` ` `    ``ver = 5; ``// Enter number of vertices``    ``edge = 6; ``// Enter number of Edges``    ``g.resize(ver);`` ` `    ``// Setting all index value of an array as 0``    ``memset``(box, 0, ``sizeof``(box)); `` ` `    ``// Enter all the end-points of all the Edges``    ``// g[x--].push_back[y--]      g[y--].push_back[x--]``    ``g.push_back(1);``    ``g.push_back(0); ``// x = 1, y = 2 ;``    ``g.push_back(2);``    ``g.push_back(1); ``// x = 2, y = 3 ;``    ``g.push_back(3);``    ``g.push_back(2); ``// x = 3, y = 4 ;``    ``g.push_back(3);``    ``g.push_back(0); ``// x = 1, y = 4 ;``    ``g.push_back(4);``    ``g.push_back(3); ``// x = 4, y = 5 ;``    ``g.push_back(4);``    ``g.push_back(2); ``// x = 3, y = 5 ;`` ` `    ``vector<``int``> S = Dominant(ver, edge);``    ``cout << ``"The Dominant Set is : { "``;``    ``for` `(``int` `i = 0; i < (``int``)S.size(); i++)``        ``cout << S[i] + 1 << ``" "``;``    ``cout << ``"}"``;``    ``return` `0;``}`

## Java

 `// Java program to find the Dominant Set of a graph``import` `java.util.*;`` ` `class` `GFG``{`` ` `static` `Vector []g;``static` `boolean` `[]box = ``new` `boolean``[``100000``];`` ` `static` `Vector Dominant(``int` `ver, ``int` `edge)``{``    ``Vector S = ``new` `Vector(); ``// set S``    ``for` `(``int` `i = ``0``; i < ver; i++) ``    ``{``        ``if` `(!box[i]) ``        ``{``            ``S.add(i);``            ``box[i] = ``true``;``            ``for` `(``int` `j = ``0``; j < (``int``)g[i].size(); j++) ``            ``{``                ``if` `(!box[g[i].get(j)])``                ``{``                    ``box[g[i].get(j)] = ``true``;``                    ``break``;``                ``}``            ``}``        ``}``    ``}``    ``return` `S;``}`` ` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `ver, edge, x, y;`` ` `    ``ver = ``5``; ``// Enter number of vertices``    ``edge = ``6``; ``// Enter number of Edges``    ``g = ``new` `Vector[ver];``    ``for` `(``int` `i = ``0``; i < ver; i++)``        ``g[i] = ``new` `Vector();`` ` ` ` `    ``// Enter all the end-points of all the Edges``    ``// g[x--].push_back[y--]     g[y--].push_back[x--]``    ``g[``0``].add(``1``);``    ``g[``1``].add(``0``); ``// x = 1, y = 2 ;``    ``g[``1``].add(``2``);``    ``g[``2``].add(``1``); ``// x = 2, y = 3 ;``    ``g[``2``].add(``3``);``    ``g[``3``].add(``2``); ``// x = 3, y = 4 ;``    ``g[``0``].add(``3``);``    ``g[``3``].add(``0``); ``// x = 1, y = 4 ;``    ``g[``3``].add(``4``);``    ``g[``4``].add(``3``); ``// x = 4, y = 5 ;``    ``g[``2``].add(``4``);``    ``g[``4``].add(``2``); ``// x = 3, y = 5 ;`` ` `    ``Vector S = Dominant(ver, edge);``    ``System.out.print(``"The Dominant Set is : { "``);``    ``for` `(``int` `i = ``0``; i < (``int``)S.size(); i++)``        ``System.out.print(S.get(i) + ``1` `+ ``" "``);``    ``System.out.print(``"}"``);``}``}`` ` `// This code is contributed by Rajput-Ji`

## C#

 `// C# program to find the Dominant Set of a graph``using` `System;``using` `System.Collections.Generic;`` ` `class` `GFG``{`` ` `static` `List<``int``> []g;``static` `bool` `[]box = ``new` `bool``;`` ` `static` `List<``int``> Dominant(``int` `ver, ``int` `edge)``{``    ``List<``int``> S = ``new` `List<``int``>(); ``// set S``    ``for` `(``int` `i = 0; i < ver; i++) ``    ``{``        ``if` `(!box[i]) ``        ``{``            ``S.Add(i);``            ``box[i] = ``true``;``            ``for` `(``int` `j = 0; j < (``int``)g[i].Count; j++) ``            ``{``                ``if` `(!box[g[i][j]])``                ``{``                    ``box[g[i][j]] = ``true``;``                    ``break``;``                ``}``            ``}``        ``}``    ``}``    ``return` `S;``}`` ` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``int` `ver, edge;`` ` `    ``ver = 5; ``// Enter number of vertices``    ``edge = 6; ``// Enter number of Edges``    ``g = ``new` `List<``int``>[ver];``    ``for` `(``int` `i = 0; i < ver; i++)``        ``g[i] = ``new` `List<``int``>();`` ` `    ``// Enter all the end-points of all the Edges``    ``// g[x--].push_back[y--]     g[y--].push_back[x--]``    ``g.Add(1);``    ``g.Add(0); ``// x = 1, y = 2 ;``    ``g.Add(2);``    ``g.Add(1); ``// x = 2, y = 3 ;``    ``g.Add(3);``    ``g.Add(2); ``// x = 3, y = 4 ;``    ``g.Add(3);``    ``g.Add(0); ``// x = 1, y = 4 ;``    ``g.Add(4);``    ``g.Add(3); ``// x = 4, y = 5 ;``    ``g.Add(4);``    ``g.Add(2); ``// x = 3, y = 5 ;`` ` `    ``List<``int``> S = Dominant(ver, edge);``    ``Console.Write(``"The Dominant Set is : { "``);``    ``for` `(``int` `i = 0; i < (``int``)S.Count; i++)``        ``Console.Write(S[i] + 1 + ``" "``);``    ``Console.Write(``"}"``);``}``}`` ` `// This code is contributed by PrinciRaj1992`
Output:
```The Dominant Set is : { 1 3 5 }
```

Reference : wiki

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