How to create an adjacency list of a directed graph in C?

问题

EDIT: No one has answered yet but I think it has to do with how I'm storing my list. Right now I'm storing every vertex in an array of nodes called G. However I think I need to make it a two dimensional array in order for me not to overwrite data in other Nodes. (This is very confusing)

As the title says I'm trying to create a directed graph. I'm running into a problem where each time I try to add a Node to the adjacency list of a vertex it is altering a previous vertex's list. For example I have a simple directed graph with these edges. (Parent , Child)

(2,1)

(3,2)

(3,4)

(5,1)

When I try to add vertex 4 to the adjacency list of vertex 3 I end up changing what vertex 2 points to. I need it go from 3 -> 2 -> 4 without altering vertex 2. I'm at a loss for how to do this. Here is my code

    Node* create_graph(Edge* E, int numbVertices, size_t size){
         int i, j=0;
         Node* G = (Node*)malloc(sizeof(Node) * numbVertices);
         G[0].vertex = 0;
         G[0].next = NULL;

         for(i=1;i<numbVertices;i++){
             G[i].e = 0;
             G[i].vertex = i;
             G[i].next = NULL;
             for(j=0;j<size;j++){
                  if((E[j].p) == i){
                  /* If a parent vertex in the list of edges E matches i
                  *value we insert child vertex (E[j].c) of that edge
                  *into the adjacency list  */
                  insert(i,G,E[j]);
                  }
             }
         }
         return G;
    }

This next function is called inside the previous function. NOTE: in insert E represents a single edge while in create_graph E represents a list of all edges

void insert(int i, Node* G, Edge E){
    Node* buffer;
    Node* new;
    new=(Node*)malloc(sizeof(Node));

    new->e = new->e + 1;
    new->next = &G[E.c]  //Here we make sure new node points to child of our edge
    new->vertex = E.p 

    int s;
    //If this is the first time the vertex is visited the 
    //adj list will be empty hence e will equal 0

    if(G[i].e == 0){
        G[i] = *new;
    }
    else{
         /* When this condition is met it means the adj list is not empty
          *and we need to go to the end of the list and add out child vertex
          *The for loop executes e times which = number of items in adj list
          */
         buffer = &G[i];
         for(s=0; s< (new->e); s++){
              buffer = buffer->next;
         }
         new->vertex = E.c;
         buffer->next = new;
    }
}

来源：https://stackoverflow.com/questions/40120088/how-to-create-an-adjacency-list-of-a-directed-graph-in-c

标签

directed-graph

adjacency-list