Added DFS algorithm

data_structures/graphs/DFS.c

@@ -0,0 +1,128 @@
+#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");
+    }
+}