Write a program to traverse a graph using breadth-first search (BFS) code example

Example 1: bfs traversal of graph in c

// BFS algorithm in C

#include <stdio.h>
#include <stdlib.h>
#define SIZE 40

struct queue {
  int items[SIZE];
  int front;
  int rear;
};

struct queue* createQueue();
void enqueue(struct queue* q, int);
int dequeue(struct queue* q);
void display(struct queue* q);
int isEmpty(struct queue* q);
void printQueue(struct queue* q);

struct node {
  int vertex;
  struct node* next;
};

struct node* createNode(int);

struct Graph {
  int numVertices;
  struct node** adjLists;
  int* visited;
};

// BFS algorithm
void bfs(struct Graph* graph, int startVertex) {
  struct queue* q = createQueue();

  graph->visited[startVertex] = 1;
  enqueue(q, startVertex);

  while (!isEmpty(q)) {
    printQueue(q);
    int currentVertex = dequeue(q);
    printf("Visited %d\n", currentVertex);

    struct node* temp = graph->adjLists[currentVertex];

    while (temp) {
      int adjVertex = temp->vertex;

      if (graph->visited[adjVertex] == 0) {
        graph->visited[adjVertex] = 1;
        enqueue(q, adjVertex);
      }
      temp = temp->next;
    }
  }
}

// Creating a node
struct node* createNode(int v) {
  struct node* newNode = malloc(sizeof(struct node));
  newNode->vertex = v;
  newNode->next = NULL;
  return newNode;
}

// Creating a graph
struct Graph* createGraph(int vertices) {
  struct Graph* graph = malloc(sizeof(struct Graph));
  graph->numVertices = vertices;

  graph->adjLists = malloc(vertices * sizeof(struct node*));
  graph->visited = malloc(vertices * sizeof(int));

  int i;
  for (i = 0; i < vertices; i++) {
    graph->adjLists[i] = NULL;
    graph->visited[i] = 0;
  }

  return graph;
}

// Add edge
void addEdge(struct Graph* graph, int src, int dest) {
  // Add edge from src to dest
  struct node* newNode = createNode(dest);
  newNode->next = graph->adjLists[src];
  graph->adjLists[src] = newNode;

  // Add edge from dest to src
  newNode = createNode(src);
  newNode->next = graph->adjLists[dest];
  graph->adjLists[dest] = newNode;
}

// Create a queue
struct queue* createQueue() {
  struct queue* q = malloc(sizeof(struct queue));
  q->front = -1;
  q->rear = -1;
  return q;
}

// Check if the queue is empty
int isEmpty(struct queue* q) {
  if (q->rear == -1)
    return 1;
  else
    return 0;
}

// Adding elements into queue
void enqueue(struct queue* q, int value) {
  if (q->rear == SIZE - 1)
    printf("\nQueue is Full!!");
  else {
    if (q->front == -1)
      q->front = 0;
    q->rear++;
    q->items[q->rear] = value;
  }
}

// Removing elements from queue
int dequeue(struct queue* q) {
  int item;
  if (isEmpty(q)) {
    printf("Queue is empty");
    item = -1;
  } else {
    item = q->items[q->front];
    q->front++;
    if (q->front > q->rear) {
      printf("Resetting queue ");
      q->front = q->rear = -1;
    }
  }
  return item;
}

// Print the queue
void printQueue(struct queue* q) {
  int i = q->front;

  if (isEmpty(q)) {
    printf("Queue is empty");
  } else {
    printf("\nQueue contains \n");
    for (i = q->front; i < q->rear + 1; i++) {
      printf("%d ", q->items[i]);
    }
  }
}

int main() {
  struct Graph* graph = createGraph(6);
  addEdge(graph, 0, 1);
  addEdge(graph, 0, 2);
  addEdge(graph, 1, 2);
  addEdge(graph, 1, 4);
  addEdge(graph, 1, 3);
  addEdge(graph, 2, 4);
  addEdge(graph, 3, 4);

  bfs(graph, 0);

  return 0;
}

Example 2: BFS AND DFS IN C

#include<stdio.h>
#include<stdlib.h>
 
#define MAX 100  
 
#define initial 1
#define waiting 2
#define visited 3
 
int n;    
int adj[MAX][MAX];
int state[MAX]; 
void create_graph();
void BF_Traversal();
void BFS(int v);
 
int queue[MAX], front = -1,rear = -1;
void insert_queue(int vertex);
int delete_queue();
int isEmpty_queue();
 
int main()
{
	create_graph();
	BF_Traversal();
	return 0;
}
 
void BF_Traversal()
{
	int v;
	
	for(v=0; v<n; v++) 
		state[v] = initial;
	
	printf("Enter Start Vertex for BFS: \n");
	scanf("%d", &v);
	BFS(v);
}
 
void BFS(int v)
{
	int i;
	
	insert_queue(v);
	state[v] = waiting;
	
	while(!isEmpty_queue())
	{
		v = delete_queue( );
		printf("%d ",v);
		state[v] = visited;
		
		for(i=0; i<n; i++)
		{
			if(adj[v][i] == 1 && state[i] == initial) 
			{
				insert_queue(i);
				state[i] = waiting;
			}
		}
	}
	printf("\n");
}
 
void insert_queue(int vertex)
{
	if(rear == MAX-1)
		printf("Queue Overflow\n");
	else
	{
		if(front == -1) 
			front = 0;
		rear = rear+1;
		queue[rear] = vertex ;
	}
}
 
int isEmpty_queue()
{
	if(front == -1 || front > rear)
		return 1;
	else
		return 0;
}
 
int delete_queue()
{
	int delete_item;
	if(front == -1 || front > rear)
	{
		printf("Queue Underflow\n");
		exit(1);
	}
	
	delete_item = queue[front];
	front = front+1;
	return delete_item;
}
 
void create_graph()
{
	int count,max_edge,origin,destin;
 
	printf("Enter number of vertices : ");
	scanf("%d",&n);
	max_edge = n*(n-1);
 
	for(count=1; count<=max_edge; count++)
	{
		printf("Enter edge %d( -1 -1 to quit ) : ",count);
		scanf("%d %d",&origin,&destin);
 
		if((origin == -1) && (destin == -1))
			break;
 
		if(origin>=n || destin>=n || origin<0 || destin<0)
		{
			printf("Invalid edge!\n");
			count--;
		}
		else
		{
			adj[origin][destin] = 1;
		}
	}
}