directed graph using adjacency list in c++ code example

Example 1: graph using djacency matrix c++

// Adjacency Matrix representation in C++

#include <iostream>
using namespace std;

class Graph {
   private:
  bool** adjMatrix;
  int numVertices;

   public:
  // Initialize the matrix to zero
  Graph(int numVertices) {
    this->numVertices = numVertices;
    adjMatrix = new bool*[numVertices];
    for (int i = 0; i < numVertices; i++) {
      adjMatrix[i] = new bool[numVertices];
      for (int j = 0; j < numVertices; j++)
        adjMatrix[i][j] = false;
    }
  }

  // Add edges
  void addEdge(int i, int j) {
    adjMatrix[i][j] = true;
    adjMatrix[j][i] = true;
  }

  // Remove edges
  void removeEdge(int i, int j) {
    adjMatrix[i][j] = false;
    adjMatrix[j][i] = false;
  }

  // Print the martix
  void toString() {
    for (int i = 0; i < numVertices; i++) {
      cout << i << " : ";
      for (int j = 0; j < numVertices; j++)
        cout << adjMatrix[i][j] << " ";
      cout << "\n";
    }
  }

  ~Graph() {
    for (int i = 0; i < numVertices; i++)
      delete[] adjMatrix[i];
    delete[] adjMatrix;
  }
};

int main() {
  Graph g(4);

  g.addEdge(0, 1);
  g.addEdge(0, 2);
  g.addEdge(1, 2);
  g.addEdge(2, 0);
  g.addEdge(2, 3);

  g.toString();
}

Example 2: Graph Adjacent Node in c++

#include <iostream>
using namespace std;

struct adjNode {
    int val, cost;
    adjNode* next;
};

struct graphEdge {
    int start_ver, end_ver, weight;
};
class DiaGraph{
   
    adjNode* getAdjListNode(int value, int weight, adjNode* head)   {
        adjNode* newNode = new adjNode;
        newNode->val = value;
        newNode->cost = weight;
         
        newNode->next = head; 
        return newNode;
    }
    int N;  
public:
    adjNode **head;          

    DiaGraph(graphEdge edges[], int n, int N)  {
     
        head = new adjNode*[N]();
        this->N = N;
       
        for (int i = 0; i < N; ++i)
            head[i] = nullptr;
      
        for (unsigned i = 0; i < n; i++)  {
            int start_ver = edges[i].start_ver;
            int end_ver = edges[i].end_ver;
            int weight = edges[i].weight;
       
            adjNode* newNode = getAdjListNode(end_ver, weight, head[start_ver]);
             
                  
            head[start_ver] = newNode;
             }
    }
   
     ~DiaGraph() {
    for (int i = 0; i < N; i++)
        delete[] head[i];
        delete[] head;
     }
};

void display_AdjList(adjNode* ptr, int i)
{
    while (ptr != nullptr) {
        cout << "(" << i << ", " << ptr->val
            << ", " << ptr->cost << ") ";
        ptr = ptr->next;
    }
    cout << endl;
}

int main()
{
    
    graphEdge edges[] = {
      
        {0,1,2},{0,2,4},{1,4,3},{2,3,2},{3,1,4},{4,3,3}
    };
    int N = 6;   
  
    int n = sizeof(edges)/sizeof(edges[0]);
   
    DiaGraph diagraph(edges, n, N);
  
    cout<<"Graph adjacency list "<<endl<<"(start_vertex, end_vertex, weight):"<<endl;
    for (int i = 0; i < N; i++)
    {
        
        display_AdjList(diagraph.head[i], i);
    }
    return 0;
}

Example 3: Oriented and unoriented graphs C++

#include <iostream>
using namespace std;
// stores adjacency list items
struct adjNode {
    int val, cost;
    adjNode* next;
};
// structure to store edges
struct graphEdge {
    int start_ver, end_ver, weight;
};
class DiaGraph{
    // insert new nodes into adjacency list from given graph
    adjNode* getAdjListNode(int value, int weight, adjNode* head)   {
        adjNode* newNode = new adjNode;
        newNode->val = value;
        newNode->cost = weight;
         
        newNode->next = head;   // point new node to current head
        return newNode;
    }
    int N;  // number of nodes in the graph
public:
    adjNode **head;                //adjacency list as array of pointers
    // Constructor
    DiaGraph(graphEdge edges[], int n, int N)  {
        // allocate new node
        head = new adjNode*[N]();
        this->N = N;
        // initialize head pointer for all vertices
        for (int i = 0; i < N; ++i)
            head[i] = nullptr;
        // construct directed graph by adding edges to it
        for (unsigned i = 0; i < n; i++)  {
            int start_ver = edges[i].start_ver;
            int end_ver = edges[i].end_ver;
            int weight = edges[i].weight;
            // insert in the beginning
            adjNode* newNode = getAdjListNode(end_ver, weight, head[start_ver]);
             
                        // point head pointer to new node
            head[start_ver] = newNode;
             }
    }
      // Destructor
     ~DiaGraph() {
    for (int i = 0; i < N; i++)
        delete[] head[i];
        delete[] head;
     }
};
// print all adjacent vertices of given vertex
void display_AdjList(adjNode* ptr, int i)
{
    while (ptr != nullptr) {
        cout << "(" << i << ", " << ptr->val
            << ", " << ptr->cost << ") ";
        ptr = ptr->next;
    }
    cout << endl;
}
// graph implementation
int main()
{
    // graph edges array.
    graphEdge edges[] = {
        // (x, y, w) -> edge from x to y with weight w
        {0,1,2},{0,2,4},{1,4,3},{2,3,2},{3,1,4},{4,3,3}
    };
    int N = 6;      // Number of vertices in the graph
    // calculate number of edges
    int n = sizeof(edges)/sizeof(edges[0]);
    // construct graph
    DiaGraph diagraph(edges, n, N);
    // print adjacency list representation of graph
    cout<<"Graph adjacency list "<<endl<<"(start_vertex, end_vertex, weight):"<<endl;
    for (int i = 0; i < N; i++)
    {
        // display adjacent vertices of vertex i
        display_AdjList(diagraph.head[i], i);
    }
    return 0;
}