Added BFS algorithm

data_structures/graphs/BFS.c

@@ -0,0 +1,188 @@
+#include <stdio.h>
+#include <stdlib.h>
+#define SIZE 40
+//Assume max size of graph is 40 nodes
+struct queue {
+    int items[SIZE];
+    int front;
+    int rear;
+};
+
+//Some declarations
+struct queue* createQueue();
+void enqueue(struct queue* q, int);
+int dequeue(struct queue* q);
+void display(struct queue* q);
+int isEmpty(struct queue* q);
+int pollQueue(struct queue* q);
+
+//Structure to create a graph node
+struct node
+{
+    int vertex;
+    struct node* next;
+};
+
+struct node* createNode(int);
+
+//Graph data structure
+struct Graph
+{
+    int numVertices;
+    struct node** adjLists;
+    int* visited;
+};
+struct Graph* createGraph(int vertices);
+void addEdge(struct Graph* graph, int src, int dest);
+void printGraph(struct Graph* graph);
+void bfs(struct Graph* graph, int startVertex);
+
+int main()
+{
+	int vertices,edges,source,i,src,dst;
+	printf("Enter the number of vertices\n");
+	scanf("%d",&vertices);
+	struct Graph* graph = createGraph(vertices);
+	printf("Enter the number of edges\n");
+	scanf("%d",&edges);
+	for(i=0; i<edges; i++)
+	{
+		printf("Edge %d \nEnter source: ",i+1);
+		scanf("%d",&src);
+		printf("Enter destination: ");
+		scanf("%d",&dst);
+		addEdge(graph, src, dst);
+	}
+	printf("Enter source of bfs\n");
+	scanf("%d",&source);
+	bfs(graph, source);
+	
+	//Uncomment below part to get a ready-made example
+    /*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;
+}
+void bfs(struct Graph* graph, int startVertex)
+ {
+    struct queue* q = createQueue();
+    
+    //Add to visited list and put in queue
+    graph->visited[startVertex] = 1;
+    enqueue(q, startVertex);
+    printf("Breadth first traversal from vertex %d is:\n",startVertex);
+    
+    //Iterate while queue not empty
+    while(!isEmpty(q)){
+        printf("%d ",pollQueue(q));
+        int currentVertex = dequeue(q);
+    
+        struct node* temp = graph->adjLists[currentVertex];
+        //Add all unvisited neighbours of current vertex to queue to be printed next
+        while(temp) {
+            int adjVertex = temp->vertex;
+            //Only add if neighbour is unvisited
+            if(graph->visited[adjVertex] == 0){
+                graph->visited[adjVertex] = 1;
+                enqueue(q, adjVertex);
+            }
+            temp = temp->next;
+       }
+    }
+}
+//Memory for a graph node 
+struct node* createNode(int v)
+{
+    struct node* newNode = malloc(sizeof(struct node));
+    newNode->vertex = v;
+    newNode->next = NULL;
+    return newNode;
+}
+//Allocates memory for graph data structure, in adjacency list format
+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;
+}
+//Adds bidirectional edge to graph 
+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; comment it out for directed graph
+    newNode = createNode(src);
+    newNode->next = graph->adjLists[dest];
+    graph->adjLists[dest] = newNode;
+}
+//Allocates memory for our queue data structure
+struct queue* createQueue() 
+{
+    struct queue* q = malloc(sizeof(struct queue));
+    q->front = -1;
+    q->rear = -1;
+    return q;
+}
+//Checks for empty queue
+int isEmpty(struct queue* q) 
+{
+    if(q->rear == -1) 
+        return 1;
+    else 
+        return 0;
+}
+//Inserts item at start of 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;
+    }
+}
+//Returns item at front of queue and removes it 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){
+            q->front = q->rear = -1;
+        }
+    }
+    return item;
+}
+
+//Returns element at front of queue
+int pollQueue(struct queue *q)
+{
+	return q->items[q->front];
+}