 # C++ Programming Code Examples

## C++ > Computer Graphics Code Examples

### C++ Program to Represent Graph Using Linked List

``` C++ Program to Represent Graph Using Linked List - This algorithm represents a graph using linked list. - The time complexity of this algorithm is O(e). - This algorithm takes the input of the number of vertex and edges. - Take the input of connected vertex pairs. - Print the adjacency list using linked list. - Exit. #include<iostream> using namespace std; // A structure to represent a node in the adjacency list. struct node { int data; struct node *link; }; // A structure to represent list of vertexes connected to the given vertex. struct vertexlist { struct node *vlisthead; }; // A structure to maintain the graph vertexes and its connections to other vertexes. struct Graph { int v; struct vertexlist *vl; }; // A function to declare the graph according to the number of vertex. struct Graph* CreateGraph(int n) { int i; struct Graph *vlist = new Graph; vlist->v = n; // declare a list for n vertex. vlist->vl = new vertexlist[n+1]; // Assign the head to NULL. for(i = 0; i < n+1; i++) { vlist->vl[i].vlisthead = NULL; } return vlist; } // A function to create a new data node. struct node* NewNode(int value) { struct node *newnode = new node; newnode->data = value; newnode->link = NULL; return newnode; } // A function to add the edge into the undirected graph. void InsertNode(Graph *G, int v1, int v2) { node *newnode1 = NewNode(v1); node *newnode2 = NewNode(v2); node *temp = new node; // Since it is undirected graph, count each edge as two connection. // Connection 1, v2 to v1. if(G->vl[v2].vlisthead == NULL) { // If the head is null insert the node to the head. G->vl[v2].vlisthead = newnode1; } else { // Otherwise, add the node at the beginning. newnode1->link = G->vl[v2].vlisthead; G->vl[v2].vlisthead = newnode1; } // Connection 2, v1 to v2. if(G->vl[v1].vlisthead == NULL) { // If the head is null insert the node to the head. G->vl[v1].vlisthead = newnode2; } else { // Otherwise, add the node at the beginning. newnode2->link = G->vl[v1].vlisthead; G->vl[v1].vlisthead = newnode2; } } int main() { int i, v, e; // Take the input of the number of vertex and edges the graph have. cout<<"Enter the number of vertexes of the graph: "; cin>>v; struct Graph *G = CreateGraph(v); cout<<"\nEnter the number of edges of the graph: "; cin>>e; int edge[e]; // Take the input of the adjacent vertex pairs of the given graph. for(i = 0; i < e; i++) { cout<<"\nEnter the vertex pair for edge "<<i+1; cout<<"\nV(1): "; cin>>edge[i]; cout<<"V(2): "; cin>>edge[i]; InsertNode(G, edge[i], edge[i]); } // Print the incidence list representation of the graph. cout<<"\n\nThe incidence list representation for the given graph: "; for(i = 0; i < v; i++) { cout<<"\n\tV("<<i+1<<") -> { "; while(G->vl[i+1].vlisthead != NULL) { cout<<G->vl[i+1].vlisthead->data<<" "; G->vl[i+1].vlisthead = G->vl[i+1].vlisthead->link; } cout<<"}"; } } ``` 