struct priority_queue *pq_new(unsigned int size, unsigned int universe) {
struct priority_queue *pq;
make_node_list(size);
pq = new_pq();
pq->init_n = size;
return pq;
}
// The "standard" version of Dijkstra's,
// ie the one that is the same as shown in the lecture
// see page 16 of lec08.pdf
// Comments starting with //* are the lines from pseudocode in page 16
// Print out the shortest paths from the source node to each other node
void dijkstras(graph_t *g, int v0) {
int v;
int u, w; double weight; // generous vars for edge (u->w,weight)
// To store current min-costs and previous vertices
int *prev; // prev[v]=u if v was reached from u
double *dist; // dist[v]= current best dist from source to v
bool *inQ; // a helping array for quick check if v in Q
assert(prev= malloc( g->n * sizeof(*prev) ) );
assert(dist= malloc( g->n * sizeof(*dist) ) );
assert(inQ= malloc( g->n * sizeof(*inQ) ) );
/* Initialization ------------------------------ */
for (v = 0; v < g->n; v++) { //* foreach v in V
prev[v] = NO_PREV; //* prev[v]= nil
dist[v] = INFINITY; //* dist[v]= infinity
}
dist[v0] = 0; //* dist[v0]=0
//* Q = InitPriorityQueue(V)
pq_t *Q = new_pq();
for (v = 0; v < g->n; v++) {
pq_enqueue(Q, v, dist[v]);
inQ[v]= true; // marks v as being inside the queue
}
/* Main loop of Dijkstra's ------------------------------ */
// buddy array of n elements to store the adjacency list of a vertex
data_t *neighbours; int n;
assert(neighbours= malloc( g->n * sizeof(*neighbours) ) );
while (!pq_is_empty(Q)) { //* while Q is non empty do
// remove min vertex
u = pq_remove_min(Q); //* u= EjectMin(Q)
inQ[u]= false; // marks u as not in Q anymore
// With this vertex u:
// first, copies the adjacency list of u to array neighbours
n= list_2_array(g->vs[u].A, neighbours);
for (v = 0; v < n; v++) { //* for each (u,w) in E do
w = neighbours[v].id; // having:edge (u-->w,weight)
weight= neighbours[v].weight;
//* if (w in Q && dist[v]+weight(u,w) <dist[v]
if ( inQ[w] && dist[w] > dist[u]+weight) {
dist[w] = dist[u]+weight; //* dist[w]= dist[u]+weight(u,v)
prev[w] = u; //* prev[w]= u
//* Update(Q, w, dist[w])
pq_update(Q, w, dist[w]);
}
}
}
/* Prints out all shortest paths ------------------------------ */
print_all_path(dist, prev, g, v0);
// free the dynamic data structures
free(dist);
free(prev);
free(neighbours);
free_pq(Q);
}
// NON-standard version of Dijkstra's:
// Print out the shortest paths from the source node to each other node
void dijkstras(graph_t *g, int source) {
int i;
int u, v; double weight; // generous vars for edge (u->v,weight)
double new_weight;
// To store current min-costs and previous vertices
int *prev; // prev[v]=u if v was reached from u
double *dist; // dist[v]= current best dist from source to v
assert(prev= malloc( g->n * sizeof(*prev) ) );
assert(dist= malloc( g->n * sizeof(*dist) ) );
/* Initialization ------------------------------ */
for (i = 0; i < g->n; i++) {
prev[i] = NO_PREV;
dist[i] = INFINITY;
}
dist[source] = 0;
// enqueue "source" - the only one that has limitted dist
pq_t *queue = new_pq();
pq_enqueue(queue, source, dist[source]);
/* Main loop of Dijkstra's ------------------------------ */
// buddy array of n elements to store the adjacency list of a vertex
data_t *neighbours; int n;
assert(neighbours= malloc( g->n * sizeof(*neighbours) ) );
while (!pq_is_empty(queue)) {
// remove min vertex
u = pq_remove_min(queue);
// With this vertex u:
// * first, copies the adjacency list of u to array neighbours
n= list_2_array(g->vs[u].A, neighbours);
// * then, inspects each of the neighbour
for (i = 0; i < n; i++) {
v = neighbours[i].id; // looking at edge (u-->v,weight)
weight = neighbours[i].weight;
new_weight = dist[u] + weight;
// if v was reached before with a better outcome
// then we just ignore the edge u-->v
if ( dist[v] <= new_weight) continue;
// updates vertex v in the queue
if (dist[v] == INFINITY) {
// if v never been reached before, adds it to queue
pq_enqueue(queue, v, new_weight);
} else {
// otherwise, updates weight of v in the queue
// note that the update must be successful
if ( !pq_update(queue, v, new_weight) ){
fprintf(stderr, "Internal error: Something wrong "
"in code or in data (such as negative weight)\n");
exit(EXIT_FAILURE);
}
}
// now updaes dist[v] and prev[v]
dist[v] = new_weight;
prev[v] = u;
}
}
/* Prints out all shortest paths ------------------------------ */
print_all_path(dist, prev, g, source);
// free the dynamic data structures
free(dist);
free(prev);
free(neighbours);
free_pq(queue);
}
