bfs.c

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

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

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

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

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

// 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 graph
void printGraph(struct Graph* graph) {
int v;
printf("\nAdjacency list of Graph:-\n");
for (v = 0; v < graph->numVertices; v++) {
struct node* temp = graph->adjLists[v];
printf(" Vertex (%d) :: ", v);
while (temp) {
printf(" -> %d", temp->vertex);
temp = temp->next;
}
printf("\n");
}
}

// 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() {
int from, to ,n, e, i, source;
printf("Enter the number of vertices: ");
scanf("%d", &n);

//Construct the Graph
struct Graph* graph = createGraph(n);

printf("Enter the number of Edges: ");
scanf("%d", &e);

for(i=1; i<=e; i++){
printf(" Enter edge-%d (v, v): ",i);
scanf("%d%d", &from,&to);
addEdge(graph, from, to);
}
printGraph(graph);

printf("\nEnter the source vertex: ");
scanf("%d", &source);

printf("\nBFS Search Path:\n");
bfs(graph, source);

return 0;
}