Add and Remove vertex in Adjacency Matrix representation of Graph (original) (raw)
Last Updated : 14 Mar, 2023
A graph is a presentation of a set of entities where some pairs of entities are linked by a connection. Interconnected entities are represented by points referred to as vertices, and the connections between the vertices are termed as edges. Formally, a graph is a pair of sets (V, E), where V is a collection of vertices, and E is a collection of edges joining a pair of vertices.
A graph can be represented by using an Adjacency Matrix.
Initialization of Graph: The adjacency matrix will be depicted using a 2D array, a constructor will be used to assign the size of the array and each element of that array will be initialized to 0. Showing that the degree of each vertex in the graph is zero.
C++ `
class Graph { private: // number of vertices int n;
// adjacency matrix
int g[10][10];public: // constructor Graph(int x) { n = x;
// initializing each element of the adjacency matrix to zero
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
g[i][j] = 0;
}
}
}};
Java
class Graph { // number of vertices private int n;
// adjacency matrix
private int[][] g = new int[10][10];
// constructor
Graph(int x)
{
this.n = x;
int i, j;
// initializing each element of the adjacency matrix to zero
for (i = 0; i < n; ++i) {
for (j = 0; j < n; ++j) {
g[i][j] = 0;
}
}
}}
Python3
class Graph: # number of vertices __n = 0
# adjacency matrix
__g =[[0 for x in range(10)] for y in range(10)]
# constructor
def __init__(self, x):
self.__n = x
# initializing each element of the adjacency matrix to zero
for i in range(0, self.__n):
for j in range(0, self.__n):
self.__g[i][j]= 0C#
class Graph{
// Number of vertices private int n;
// Adjacency matrix private int[,] g = new int[10, 10];
// Constructor Graph(int x) { this.n = x; int i, j;
// Initializing each element of
// the adjacency matrix to zero
for(i = 0; i < n; ++i)
{
for(j = 0; j < n; ++j)
{
g[i, j] = 0;
}
}} }
// This code is contributed by ukasp
JavaScript
class Graph { constructor(x) { // number of vertices this.n = x;
// adjacency matrix
this.g = [];
// initializing each element of the adjacency matrix to zero
for (let i = 0; i < this.n; ++i) {
this.g[i] = [];
for (let j = 0; j < this.n; ++j) {
this.g[i][j] = 0;
}
}
}}
`
Here the adjacency matrix is g[n][n] in which the degree of each vertex is zero.
Displaying the Graph: The graph is depicted using the adjacency matrix g[n][n] having the number of vertices n. The 2D array(adjacency matrix) is displayed in which if there is an edge between two vertices 'x' and 'y' then g[x][y] is 1 otherwise 0.
C++ `
void displayAdjacencyMatrix() { cout << "\n\n Adjacency Matrix:";
// displaying the 2D array
for (int i = 0; i < n; ++i) {
cout << "\n";
for (int j = 0; j < n; ++j) {
cout << " " << g[i][j];
}
}}
Java
public void displayAdjacencyMatrix() { System.out.print("\n\n Adjacency Matrix:");
// displaying the 2D array
for (int i = 0; i < n; ++i) {
System.out.println();
for (int j = 0; j < n; ++j) {
System.out.print(" " + g[i][j]);
}
}}
Python3
def displayAdjacencyMatrix(self): print("\n\n Adjacency Matrix:", end ="")
# displaying the 2D array
for i in range(0, self.__n):
print()
for j in range(0, self.__n):
print("", self.__g[i][j], end ="")C#
public void DisplayAdjacencyMatrix() { Console.Write("\n\n Adjacency Matrix:");
// Displaying the 2D array
for (int i = 0; i < n; ++i)
{
Console.WriteLine();
for (int j = 0; j < n; ++j)
{
Console.Write(" " + g[i,j]);
}
}}
JavaScript
function displayAdjacencyMatrix() { console.log("\n\n Adjacency Matrix:");
// displaying the 2D array
for (let i = 0; i < n; ++i) {
let row = "";
for (let j = 0; j < n; ++j) {
row += " " + g[i][j];
}
console.log(row);
}}
`
The above method is a public member function of the class Graph which displays the graph using an adjacency matrix.
Adding Edges between Vertices in the Graph: To add edges between two existing vertices such as vertex 'x' and vertex 'y' then the elements g[x][y] and g[y][x] of the adjacency matrix will be assigned to 1, depicting that there is an edge between vertex 'x' and vertex 'y'.
C++ `
void addEdge(int x, int y) {
// checks if the vertex exists in the graph
if ((x >= n) || (y > n)) {
cout << "Vertex does not exists!";
}
// checks if the vertex is connecting to itself
if (x == y) {
cout << "Same Vertex!";
}
else {
// connecting the vertices
g[y][x] = 1;
g[x][y] = 1;
}}
Java
public void addEdge(int x, int y) { // checks if the vertex exists in the graph if ((x >= n) || (y > n)) { System.out.println("Vertex does not exists!"); }
// checks if the vertex is connecting to itself
if (x == y) {
System.out.println("Same Vertex!");
}
else {
// connecting the vertices
g[y][x] = 1;
g[x][y] = 1;
}}
Python3
def addEdge(self, x, y):
# checks if the vertex exists in the graph
if(x>= self.__n) or (y >= self.__n):
print("Vertex does not exists !")
# checks if the vertex is connecting to itself
if(x == y):
print("Same Vertex !")
else:
# connecting the vertices
self.__g[y][x]= 1
self.__g[x][y]= 1C#
public void AddEdge(int x, int y) { // checks if the vertex exists in the graph if ((x >= n) || (y > n)) { Console.WriteLine("Vertex does not exists!"); }
// checks if the vertex is connecting to itself if (x == y) { Console.WriteLine("Same Vertex!"); } else { // connecting the vertices g[y, x] = 1; g[x, y] = 1; } }
JavaScript
function addEdge(x, y) {
// checks if the vertex exists in the graph
if ((x >= n) || (y > n)) {
console.log("Vertex does not exist!");
}
// checks if the vertex is connecting to itself
if (x === y) {
console.log("Same Vertex!");
}
else {
// connecting the vertices
g[y][x] = 1;
g[x][y] = 1;
}}
`
Here the above method is a public member function of the class Graph which connects any two existing vertices in the Graph.
Adding a Vertex in the Graph: To add a vertex in the graph, we need to increase both the row and column of the existing adjacency matrix and then initialize the new elements related to that vertex to 0.(i.e the new vertex added is not connected to any other vertex)
C++ `
void addVertex() { // increasing the number of vertices n++; int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i) {
g[i][n - 1] = 0;
g[n - 1][i] = 0;
}}
Java
public void addVertex() { // increasing the number of vertices n++; int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i) {
g[i][n - 1] = 0;
g[n - 1][i] = 0;
}}
Python3
def addVertex(self):
# increasing the number of vertices
self.__n = self.__n + 1;
# initializing the new elements to 0
for i in range(0, self.__n):
self.__g[i][self.__n-1]= 0
self.__g[self.__n-1][i]= 0JavaScript
function addVertex() { // increasing the number of vertices n++; let i;
// initializing the new elements to 0 for (i = 0; i < n; ++i) { g[i][n - 1] = 0; g[n - 1][i] = 0; } }
C#
public void addVertex() { // increasing the number of vertices n++; int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i) {
g[i, n - 1] = 0;
g[n - 1, i] = 0;
}}
`
The above method is a public member function of the class Graph which increments the number of vertices by 1 and the degree of the new vertex is 0.
Removing a Vertex in the Graph: To remove a vertex from the graph, we need to check if that vertex exists in the graph or not and if that vertex exists then we need to shift the rows to the left and the columns upwards of the adjacency matrix so that the row and column values of the given vertex gets replaced by the values of the next vertex and then decrease the number of vertices by 1.In this way that particular vertex will be removed from the adjacency matrix.
C++ `
void removeVertex(int x) { // checking if the vertex is present if (x > n) { cout << "\nVertex not present!"; return; } else { int i;
// removing the vertex
while (x < n) {
// shifting the rows to left side
for (i = 0; i < n; ++i) {
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i) {
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;
}}
Java
public void removeVertex(int x) { // checking if the vertex is present if (x > n) { System.out.println("Vertex not present!"); return; } else { int i;
// removing the vertex
while (x < n) {
// shifting the rows to left side
for (i = 0; i < n; ++i) {
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i) {
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;
}}
Python3
def removeVertex(self, x):
# checking if the vertex is present
if(x>self.__n):
print("Vertex not present !")
else:
# removing the vertex
while(x<self.__n):
# shifting the rows to left side
for i in range(0, self.__n):
self.__g[i][x]= self.__g[i][x + 1]
# shifting the columns upwards
for i in range(0, self.__n):
self.__g[x][i]= self.__g[x + 1][i]
x = x + 1
# decreasing the number of vertices
self.__n = self.__n - 1C#
public void RemoveVertex(int x) { // checking if the vertex is present if (x > n) { Console.WriteLine("Vertex not present!"); return; } else { int i;
// removing the vertex
while (x < n) {
// shifting the rows to left side
for (i = 0; i < n; ++i) {
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i) {
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;
}}
JavaScript
function removeVertex(x) { // checking if the vertex is present if (x > n) { console.log("\nVertex not present!"); return; } else { let i;
// removing the vertex
while (x < n) {
// shifting the rows to left side
for (i = 0; i < n; ++i) {
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i) {
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;} }
`
The above method is a public member function of the class Graph which removes an existing vertex from the graph by shifting the rows to the left and shifting the columns up to replace the row and column values of that vertex with the next vertex and then decreases the number of vertices by 1 in the graph.
Following is a complete program that uses all of the above methods in a Graph.
C++ `
// C++ program to add and remove Vertex in Adjacency Matrix
#include
using namespace std;
class Graph { private: // number of vertices int n;
// adjacency matrix
int g[10][10];public: // constructor Graph(int x) { n = x;
// initializing each element of the adjacency matrix to zero
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
g[i][j] = 0;
}
}
}
void displayAdjacencyMatrix()
{
cout << "\n\n Adjacency Matrix:";
// displaying the 2D array
for (int i = 0; i < n; ++i) {
cout << "\n";
for (int j = 0; j < n; ++j) {
cout << " " << g[i][j];
}
}
}
void addEdge(int x, int y)
{
// checks if the vertex exists in the graph
if ((x >= n) || (y > n)) {
cout << "Vertex does not exists!";
}
// checks if the vertex is connecting to itself
if (x == y) {
cout << "Same Vertex!";
}
else {
// connecting the vertices
g[y][x] = 1;
g[x][y] = 1;
}
}
void addVertex()
{
// increasing the number of vertices
n++;
int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i) {
g[i][n - 1] = 0;
g[n - 1][i] = 0;
}
}
void removeVertex(int x)
{
// checking if the vertex is present
if (x > n) {
cout << "\nVertex not present!";
return;
}
else {
int i;
// removing the vertex
while (x < n) {
// shifting the rows to left side
for (i = 0; i < n; ++i) {
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i) {
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;
}
}};
int main() { // creating objects of class Graph Graph obj(4);
// calling methods
obj.addEdge(0, 1);
obj.addEdge(0, 2);
obj.addEdge(1, 2);
obj.addEdge(2, 3);
// the adjacency matrix created
obj.displayAdjacencyMatrix();
// adding a vertex to the graph
obj.addVertex();
// connecting that vertex to other existing vertices
obj.addEdge(4, 1);
obj.addEdge(4, 3);
// the adjacency matrix with a new vertex
obj.displayAdjacencyMatrix();
// removing an existing vertex in the graph
obj.removeVertex(1);
// the adjacency matrix after removing a vertex
obj.displayAdjacencyMatrix();
return 0;}
Java
// Java program to add and remove Vertex in Adjacency Matrix class Graph { // number of vertices private int n;
// adjacency matrix
private int[][] g = new int[10][10];
// constructor
Graph(int x)
{
this.n = x;
int i, j;
// initializing each element of
// the adjacency matrix to zero
for (i = 0; i < n; ++i)
{
for (j = 0; j < n; ++j)
{
g[i][j] = 0;
}
}
}
public void displayAdjacencyMatrix()
{
System.out.print("\n\n Adjacency Matrix:");
// displaying the 2D array
for (int i = 0; i < n; ++i)
{
System.out.println();
for (int j = 0; j < n; ++j)
{
System.out.print(" " + g[i][j]);
}
}
}
public void addEdge(int x, int y)
{
// checks if the vertex exists in the graph
if ((x >= n) || (y > n))
{
System.out.println("Vertex does not exists!");
}
// checks if the vertex is connecting to itself
if (x == y)
{
System.out.println("Same Vertex!");
}
else
{
// connecting the vertices
g[y][x] = 1;
g[x][y] = 1;
}
}
public void addVertex()
{
// increasing the number of vertices
n++;
int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i)
{
g[i][n - 1] = 0;
g[n - 1][i] = 0;
}
}
public void removeVertex(int x)
{
// checking if the vertex is present
if (x > n)
{
System.out.println("Vertex not present!");
return;
}
else
{
int i;
// removing the vertex
while (x < n)
{
// shifting the rows to left side
for (i = 0; i < n; ++i)
{
g[i][x] = g[i][x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i)
{
g[x][i] = g[x + 1][i];
}
x++;
}
// decreasing the number of vertices
n--;
}
}}
class Main { public static void main(String[] args) { // creating objects of class Graph Graph obj = new Graph(4);
// calling methods
obj.addEdge(0, 1);
obj.addEdge(0, 2);
obj.addEdge(1, 2);
obj.addEdge(2, 3);
// the adjacency matrix created
obj.displayAdjacencyMatrix();
// adding a vertex to the graph
obj.addVertex();
// connecting that vertex to other existing vertices
obj.addEdge(4, 1);
obj.addEdge(4, 3);
// the adjacency matrix with a new vertex
obj.displayAdjacencyMatrix();
// removing an existing vertex in the graph
obj.removeVertex(1);
// the adjacency matrix after removing a vertex
obj.displayAdjacencyMatrix();
}}
Python3
Python program to add and remove Vertex in Adjacency Matrix
class Graph: # number of vertices __n = 0
# adjacency matrix
__g =[[0 for x in range(10)] for y in range(10)]
# constructor
def __init__(self, x):
self.__n = x
# initializing each element of the adjacency matrix to zero
for i in range(0, self.__n):
for j in range(0, self.__n):
self.__g[i][j]= 0
def displayAdjacencyMatrix(self):
print("\n\n Adjacency Matrix:", end ="")
# displaying the 2D array
for i in range(0, self.__n):
print()
for j in range(0, self.__n):
print("", self.__g[i][j], end ="")
def addEdge(self, x, y):
# checks if the vertex exists in the graph
if(x>= self.__n) or (y >= self.__n):
print("Vertex does not exists !")
# checks if the vertex is connecting to itself
if(x == y):
print("Same Vertex !")
else:
# connecting the vertices
self.__g[y][x]= 1
self.__g[x][y]= 1
def addVertex(self):
# increasing the number of vertices
self.__n = self.__n + 1;
# initializing the new elements to 0
for i in range(0, self.__n):
self.__g[i][self.__n-1]= 0
self.__g[self.__n-1][i]= 0
def removeVertex(self, x):
# checking if the vertex is present
if(x>self.__n):
print("Vertex not present !")
else:
# removing the vertex
while(x<self.__n):
# shifting the rows to left side
for i in range(0, self.__n):
self.__g[i][x]= self.__g[i][x + 1]
# shifting the columns upwards
for i in range(0, self.__n):
self.__g[x][i]= self.__g[x + 1][i]
x = x + 1
# decreasing the number of vertices
self.__n = self.__n - 1 creating objects of class Graph
obj = Graph(4);
calling methods
obj.addEdge(0, 1); obj.addEdge(0, 2); obj.addEdge(1, 2); obj.addEdge(2, 3);
the adjacency matrix created
obj.displayAdjacencyMatrix();
adding a vertex to the graph
obj.addVertex();
connecting that vertex to other existing vertices
obj.addEdge(4, 1); obj.addEdge(4, 3);
the adjacency matrix with a new vertex
obj.displayAdjacencyMatrix();
removing an existing vertex in the graph
obj.removeVertex(1);
the adjacency matrix after removing a vertex
obj.displayAdjacencyMatrix();
C#
// C# program to add and remove Vertex in Adjacency Matrix using System;
public class Graph { // number of vertices private int n;
// adjacency matrix
private int[,] g = new int[10, 10];
// constructor
public Graph(int x)
{
this.n = x;
int i, j;
// initializing each element of the adjacency matrix to zero
for (i = 0; i < n; ++i)
{
for (j = 0; j < n; ++j)
{
g[i, j] = 0;
}
}
}
public void displayAdjacencyMatrix()
{
Console.Write("\n\n Adjacency Matrix:");
// displaying the 2D array
for (int i = 0; i < n; ++i)
{
Console.WriteLine();
for (int j = 0; j < n; ++j)
{
Console.Write(" " + g[i, j]);
}
}
}
public void addEdge(int x, int y)
{
// checks if the vertex exists in the graph
if ((x >= n) || (y > n))
{
Console.WriteLine("Vertex does not exists!");
}
// checks if the vertex is connecting to itself
if (x == y)
{
Console.WriteLine("Same Vertex!");
}
else
{
// connecting the vertices
g[y, x] = 1;
g[x, y] = 1;
}
}
public void addVertex()
{
// increasing the number of vertices
n++;
int i;
// initializing the new elements to 0
for (i = 0; i < n; ++i)
{
g[i, n - 1] = 0;
g[n - 1, i] = 0;
}
}
public void removeVertex(int x)
{
// checking if the vertex is present
if (x > n)
{
Console.WriteLine("Vertex not present!");
return;
}
else
{
int i;
// removing the vertex
while (x < n)
{
// shifting the rows to left side
for (i = 0; i < n; ++i)
{
g[i, x] = g[i, x + 1];
}
// shifting the columns upwards
for (i = 0; i < n; ++i)
{
g[x, i] = g[x + 1, i];
}
x++;
}
// decreasing the number of vertices
n--;
}
}}
public class GFG { // Driver code public static void Main(String[] args) { // creating objects of class Graph Graph obj = new Graph(4);
// calling methods
obj.addEdge(0, 1);
obj.addEdge(0, 2);
obj.addEdge(1, 2);
obj.addEdge(2, 3);
// the adjacency matrix created
obj.displayAdjacencyMatrix();
// adding a vertex to the graph
obj.addVertex();
// connecting that vertex to other existing vertices
obj.addEdge(4, 1);
obj.addEdge(4, 3);
// the adjacency matrix with a new vertex
obj.displayAdjacencyMatrix();
// removing an existing vertex in the graph
obj.removeVertex(1);
// the adjacency matrix after removing a vertex
obj.displayAdjacencyMatrix();
}}
// This code is contributed by PrinciRaj1992
JavaScript
`
Output:
Adjacency Matrix: 0 1 1 0 1 0 1 0 1 1 0 1 0 0 1 0
Adjacency Matrix: 0 1 1 0 0 1 0 1 0 1 1 1 0 1 0 0 0 1 0 1 0 1 0 1 0
Adjacency Matrix: 0 1 0 0 1 0 1 0 0 1 0 1 0 0 1 0
Adjacency matrices waste a lot of memory space. Such matrices are found to be very sparse. This representation requires space for n*n elements, the time complexity of the addVertex() method is O(n), and the time complexity of the removeVertex() method is O(n*n) for a graph of n vertices.
From the output of the program, the Adjacency Matrix is:
And the Graph depicted by the above Adjacency Matrix is:
