TheAlgorithms-C/data_structures/graphs/DFS.c

#include <stdio.h>
#include <stdlib.h>

//A vertex of the graph 
struct node
{
    int vertex;
    struct node* next;
};
//Some declarations
struct node* createNode(int v);
struct Graph
{
    int numVertices;
    int* visited;
    struct node** adjLists; // we need int** to store a two dimensional array. Similary, we need struct node** to store an array of Linked lists
};
struct Graph* createGraph(int);
void addEdge(struct Graph*, int, int);
void printGraph(struct Graph*);
void dfs(struct Graph*, int);

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 DFS\n");
	scanf("%d",&source);
	printf("DFS from %d is:\n",source);
	dfs(graph, source);
	printf("\n");
	
	//Uncomment below part to get a ready-made example
    /*struct Graph* graph = createGraph(4);
    addEdge(graph, 0, 1);
    addEdge(graph, 0, 2);
    addEdge(graph, 1, 2);
    addEdge(graph, 2, 3);
    printf("DFS from 0 is:\n");
    dfs(graph,0);
	printf("\n");*/
    
    return 0;
}
//Recursive dfs approach
void dfs(struct Graph* graph, int vertex) {
        struct node* adjList = graph->adjLists[vertex];
        struct node* temp = adjList;
        
        //Add vertex to visited list and print it
        graph->visited[vertex] = 1;
        printf("%d ", vertex);
        
        //Recursively call the dfs function on all unvisited neighbours
        while(temp!=NULL) {
            int connectedVertex = temp->vertex;
            if(graph->visited[connectedVertex] == 0) {
                dfs(graph, connectedVertex);
            }
            temp = temp->next;
        }       
}
 //Allocate memory for a node
struct node* createNode(int v)
{
    struct node* newNode = malloc(sizeof(struct node));
    newNode->vertex = v;
    newNode->next = NULL;
    return newNode;
}
//Allocate memory for the entire graph structure
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;
}
//Creates a bidirectional 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
    newNode = createNode(src);
    newNode->next = graph->adjLists[dest];
    graph->adjLists[dest] = newNode;
}
//Utility function to see state of graph at a given time 
void printGraph(struct Graph* graph)
{
    int v;
    for (v = 0; v < graph->numVertices; v++)
    {
        struct node* temp = graph->adjLists[v];
        printf("\n Adjacency list of vertex %d\n ", v);
        while (temp)
        {
            printf("%d -> ", temp->vertex);
            temp = temp->next;
        }
        printf("\n");
    }
}