Deleting multiple occurring edges in a graph

Question

I am trying to delete the multiple occurring edges in a graph. Each vertex in the graph can have multiple outgoing edges to the same destination. like this one (this is the adjacency list). For example there are 2 connection from (3 --> 2). The numbers in the parenthesis are showing the distance, cost and time for each edge. In this case, I want to delete all the edges that have longer times. for example the first line second connection, which takes 45 hours.

### 3 -> 2 (50-300-40) ---> 2 (55-450-45) ---> 4 (45-450-45) ---> 4 (75-600-60) ---> 1 (40-450-40) ---> 1 (85-750-90) ---> NULL
### 2 -> 1 (50-450-45) ---> 3 (45-300-30) ---> 4 (80-700-80) ---> NULL
### 4 -> 2 (55-535-60) ---> 3 (75-545-65) ---> 4 (20-200-20) ---> NULL

void delete_edge(graph *g, int source_no, int dest_no) {
    // Find the source vertex
    node *source_vertex = &g->heads[source_no];
    list_node *current = source_vertex->head;
    list_node *prev = NULL;

    // Create a new adjacency list
    list_node *new_head = NULL;
    list_node *new_tail = NULL;

    // Traverse the adjacency list of the source vertex
    while (current != NULL) {
        if (current->index_of_item == dest_no) {
            // Found the edge to delete, skip it
            list_node *temp = current;
            current = current->next;
            free(temp);

            if (prev != NULL) {
                prev->next = current;
            } else {
                source_vertex->head = current;
            }
        } else {
            // Add the current edge to the new adjacency list
            if (new_head == NULL) {
                new_head = current;
                new_tail = current;
            } else {
                new_tail->next = current;
                new_tail = current;
            }

            prev = current;
            current = current->next;
        }
    }

    // Set the next pointer of the new tail to NULL
    if (new_tail != NULL) {
        new_tail->next = NULL;
    }
}



void bfs_delte_version(graph *g) {
    // Initialize the color of all vertices as White
    for (int i = 0; i < g->number_of_vertices; i++) {
        g->heads[i].color = White;
    }

    // Start BFS from the first node (source)
    node *source = &g->heads[0];
    source->color = Gray;

    queue *q = make_queue();
    enqueue(q, source);

    while (!is_empty_queue(q)) {
        queue_node *u = dequeue(q);
        list_node *temp = u->n->head;

        while (temp != NULL) {
            if (g->heads[temp->index_of_item].color == White) {
                g->heads[temp->index_of_item].color = Gray;
                enqueue(q, &g->heads[temp->index_of_item]);
            } else {
                // Delete multiple occurring edges
                delete_edge(g, u->n->data, temp->index_of_item);
            }

            temp = temp->next;
        }

        u->n->color = Black;
        printf("%d\n", u->n->data);
    }
}

I have changed my strategy to traverse the graph using BFS and then delete the edges, but I cannot figure out why it doesn't work. When called on a single edge, it doesn't change the graph, and when called on BFS traversal I get segmentation fault. I will appreciate your help

The code you have posted is incomplete.

ravenspoint
– ravenspoint

2023-06-10 18:46:39 +00:00
Commented Jun 10, 2023 at 18:46 — ravenspoint
– ravenspoint, Commented Jun 10, 2023 at 18:46

ravenspoint · Accepted Answer · 2023-06-10 18:51:42Z

0

// comparing every other times in other edges to min time
// if their time is more than minimum delete them
// else update the minimum time and delete the current edge
list_node *current = g -> heads[source].head;
while(current != NULL){
    if((current -> time) > (min_time)){
        // first moving the current and (current_next) pointers one ahead
        current -> next = current -> next -> next;
        current = current -> next;

        // assigning the worst edge
        worst_edge = current;

        // deleting the worst edge
        free(worst_edge);

        // don't make it outside the loop so that it won't update the current pointer again
        continue;


    }


    // update the current pointer
    current = current -> next;
}

You have not implemented the else branch

answered Jun 10, 2023 at 18:51

ravenspoint

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