# Maximum and minimum isolated vertices in a graph

• Last Updated : 18 Jun, 2021

Given ‘n’ vertices and ‘m’ edges of a graph. Find the minimum number and maximum number of isolated vertices that are possible in the graph.
Examples:

```Input : 4 2
Output : Minimum 0
Maximum 1

1--2 3--4 <---Minimum -  No isolated vertex
1--2   <--- Maximum - 1 Isolated vertex i.e. 4
|
3

Input : 5 2
Output : Minimum 1
Maximum 2

1--2 3--4 5  <-- Minimum - 1 isolated vertex i.e. 5
1--2   4  5  <-- Maximum - 2 isolated vertex i.e. 4 and 5
|
3```

1. For minimum number of isolated vertices, we connect two vertices by only one edge. Each vertex should be only connected to one other vertex and each vertex should have degree one
Thus if the number of edges is ‘m’, and if ‘n’ vertices <=2 * ‘m’ edges, there is no isolated vertex and if this condition is false, there are n-2*m isolated vertices.
2. For maximum number of isolated vertices, we create a polygon such that each vertex is connected to other vertex and each vertex has a diagonal with every other vertex. Thus, number of diagonals from one vertex to other vertex of n sided polygon is n*(n-3)/2 and number of edges connecting adjacent vertices is n. Thus, total number of edges is n*(n-1)/2.

Below is the implementation of above approach.

## C++

 `// CPP program to find maximum/minimum number``// of isolated vertices.``#include ``using` `namespace` `std;` `// Function to find out the minimum and``// maximum number of isolated vertices``void` `find(``int` `n, ``int` `m)``{``    ``// Condition to find out minimum number``    ``// of isolated vertices``    ``if` `(n <= 2 * m)``        ``cout << ``"Minimum "` `<< 0 << endl;``    ``else``        ``cout << ``"Minimum "` `<< n - 2 * m << endl;` `    ``// To find out maximum number of isolated``    ``// vertices``    ``// Loop to find out value of number of``    ``// vertices that are connected``    ``int` `i;``    ``for` `(i = 1; i <= n; i++) {``        ``if` `(i * (i - 1) / 2 >= m)``            ``break``;``    ``}``    ``cout << ``"Maximum "` `<< n - i;``}` `// Driver Function``int` `main()``{``    ``// Number of vertices``    ``int` `n = 4;` `    ``// Number of edges``    ``int` `m = 2;` `    ``// Calling the function to maximum and``    ``// minimum number of isolated vertices``    ``find(n, m);``    ``return` `0;``}`

## Java

 `// Java program to find maximum/minimum number``// of isolated vertices.` `import` `java.io.*;` `class` `GFG {`` `  `// Function to find out the minimum and``// maximum number of isolated vertices`` ``static` `void` `find(``int` `n, ``int` `m)``{``    ``// Condition to find out minimum number``    ``// of isolated vertices``    ``if` `(n <= ``2` `* m)``        ``System.out.println( ``"Minimum "` `+ ``0``);``    ``else``        ``System.out.println( ``"Minimum "` `+ (n - ``2` `* m));` `    ``// To find out maximum number of isolated``    ``// vertices``    ``// Loop to find out value of number of``    ``// vertices that are connected``    ``int` `i;``    ``for` `(i = ``1``; i <= n; i++) {``        ``if` `(i * (i - ``1``) / ``2` `>= m)``            ``break``;``    ``}``    ``System.out.println( ``"Maximum "` `+ (n - i));``}` `// Driver Function` `    ``public` `static` `void` `main (String[] args) {``    ` `    ``// Number of vertices``    ``int` `n = ``4``;` `    ``// Number of edges``    ``int` `m = ``2``;` `    ``// Calling the function to maximum and``    ``// minimum number of isolated vertices``    ``find(n, m);``    ``}``}``//This code is contributed by inder_verma.`

## Python3

 `# Python3 program to find maximum/minimum``# number of isolated vertices.` `# Function to find out the minimum and``# maximum number of isolated vertices``def` `find(n, m) :` `    ``# Condition to find out minimum``    ``# number of isolated vertices``    ``if` `(n <``=` `2` `*` `m):``        ``print``(``"Minimum "``, ``0``)``    ``else``:``        ``print``(``"Minimum "``, n ``-` `2` `*` `m )` `    ``# To find out maximum number of``    ``# isolated vertices``    ``# Loop to find out value of number``    ``# of vertices that are connected``    ``for` `i ``in` `range``(``1``, n ``+` `1``):``        ``if` `(i ``*` `(i ``-` `1``) ``/``/` `2` `>``=` `m):``            ``break``    ` `    ``print``(``"Maximum "``, n ``-` `i)``    ` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``# Number of vertices``    ``n ``=` `4` `    ``# Number of edges``    ``m ``=` `2` `    ``# Calling the function to maximum and``    ``# minimum number of isolated vertices``    ``find(n, m)` `# This code is contributed by``# SHUBHAMSINGH10`

## C#

 `// C# program to find maximum/``// minimum number of isolated vertices.``using` `System;` `class` `GFG``{` `// Function to find out the``// minimum and maximum number``// of isolated vertices``static` `void` `find(``int` `n, ``int` `m)``{``    ``// Condition to find out minimum``    ``// number of isolated vertices``    ``if` `(n <= 2 * m)``        ``Console.WriteLine(``"Minimum "` `+ 0);``    ``else``        ``Console.WriteLine(``"Minimum "` `+``                         ``(n - 2 * m));` `    ``// To find out maximum number``    ``// of isolated vertices``    ``// Loop to find out value of``    ``// number of vertices that``    ``// are connected``    ``int` `i;``    ``for` `(i = 1; i <= n; i++)``    ``{``        ``if` `(i * (i - 1) / 2 >= m)``            ``break``;``    ``}``    ``Console.WriteLine(``"Maximum "` `+ (n - i));``}` `// Driver Code``public` `static` `void` `Main ()``{` `    ``// Number of vertices``    ``int` `n = 4;``    ` `    ``// Number of edges``    ``int` `m = 2;``    ` `    ``// Calling the function to ``    ``// maximum and minimum number``    ``// of isolated vertices``    ``find(n, m);``}``}` `// This code is contributed``// by inder_verma.`

## PHP

 `= ``\$m``)``            ``break``;``    ``}``    ``echo` `"Maximum "` `, (``\$n` `- ``\$i``);``}` `// Driver Code` `// Number of vertices``\$n` `= 4;` `// Number of edges``\$m` `= 2;` `// Calling the function to``// maximum and minimum number``// of isolated vertices``find(``\$n``, ``\$m``);` `// This code is contributed``// by inder_verma``?>`

## Javascript

 ``

Output:

```Minimum 0
Maximum 1```

Time Complexity – O(n)

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