Added graph algorithms

Graph Algorithms/Breadth First Search.c

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+// Breadth First Search Algorithm in C
+
+#include <stdio.h>
+#include <stdlib.h>
+#define SIZE 50
+
+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;
+};
+
+// Breadth First Search  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 an  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(5);
+  addEdge(graph, 0, 1);
+  addEdge(graph, 0, 2);
+  addEdge(graph, 1, 2);
+  addEdge(graph, 1, 4);
+  addEdge(graph, 1, 3);
+  addEdge(graph, 2, 4);
+
+
+  bfs(graph, 0);
+
+  return 0;
+}

Graph Algorithms/Depth First Search.c

@@ -0,0 +1,104 @@
+// Depth first search algorithm in C
+
+#include <stdio.h>
+#include <stdlib.h>
+
+struct node {
+  int vertex;
+  struct node* next;
+};
+
+struct node* createNode(int v);
+
+struct Graph {
+  int numVertices;
+  int* visited;
+
+  // We need int** to store a two dimensional array.
+  // Similary, we need struct node** to store an array of Linked lists
+  struct node** adjLists;
+};
+
+// Depth first search algo
+void DFS(struct Graph* graph, int vertex) {
+  struct node* adjList = graph->adjLists[vertex];
+  struct node* temp = adjList;
+
+  graph->visited[vertex] = 1;
+  printf("Visited %d \n", vertex);
+
+  while (temp != NULL) {
+    int connectedVertex = temp->vertex;
+
+    if (graph->visited[connectedVertex] == 0) {
+      DFS(graph, connectedVertex);
+    }
+    temp = temp->next;
+  }
+}
+
+// Create a node
+struct node* createNode(int v) {
+  struct node* newNode = malloc(sizeof(struct node));
+  newNode->vertex = v;
+  newNode->next = NULL;
+  return newNode;
+}
+
+// Create 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;
+}
+
+// Print the graph
+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");
+  }
+}
+
+int main() {
+  struct Graph* graph = createGraph(4);
+  addEdge(graph, 0, 1);
+  addEdge(graph, 0, 2);
+  addEdge(graph, 1, 2);
+  addEdge(graph, 2, 3);
+
+  printGraph(graph);
+
+  DFS(graph, 2);
+
+  return 0;
+}