void Vertex::decrease_distance_in_heap(Vertex **heap) {
Vertex **p, **h;
- // There is some beauty in that
h = heap_slot;
- while(h > heap &&
- (p = heap + (h - heap + 1) / 2 - 1,
- (*p)->distance_from_source > (*h)->distance_from_source)) {
+ while(1) {
+ if(h <= heap) break;
+ p = heap + ((h - heap + 1) >> 1) - 1;
+ if((*p)->distance_from_source <= distance_from_source) break;
+ swap((*p)->heap_slot, heap_slot);
swap(*p, *h);
- swap((*p)->heap_slot, (*h)->heap_slot);
h = p;
}
}
void Vertex::increase_distance_in_heap(Vertex **heap, Vertex **heap_bottom) {
Vertex **c1, **c2, **h;
- // omg, that's beautiful
h = heap_slot;
- while(c1 = heap + 2 * (h - heap) + 1,
- c1 < heap_bottom &&
- (c2 = c1 + 1,
- (*c1)->distance_from_source < (*h)->distance_from_source
- ||
- (c2 < heap_bottom && (*c2)->distance_from_source < (*h)->distance_from_source)
- )) {
- if(c2 < heap_bottom && (*c2)->distance_from_source <= (*c1)->distance_from_source) {
- swap(*c2, *h);
- swap((*c2)->heap_slot, (*h)->heap_slot);
- h = c2;
+ while(1) {
+ c1 = heap + 2 * (h - heap) + 1;
+ if(c1 >= heap_bottom) break;
+ c2 = c1 + 1;
+ if((*c1)->distance_from_source < distance_from_source) {
+ if(c2 < heap_bottom && (*c2)->distance_from_source < (*c1)->distance_from_source) {
+ swap((*c2)->heap_slot, heap_slot);
+ swap(*c2, *h);
+ h = c2;
+ } else {
+ swap((*c1)->heap_slot, heap_slot);
+ swap(*c1, *h);
+ h = c1;
+ }
} else {
- swap(*c1, *h);
- swap((*c1)->heap_slot, (*h)->heap_slot);
- h = c1;
+ if(c2 < heap_bottom && (*c2)->distance_from_source < distance_from_source) {
+ swap((*c2)->heap_slot, heap_slot);
+ swap(*c2, *h);
+ h = c2;
+ } else break;
}
}
}
// pred_edge_toward_source.
void MTPGraph::find_shortest_path() {
+ int heap_size;
Vertex *v, *tv, **last_slot;
Edge *e;
scalar_t d;
_vertices[k].pred_edge_toward_source = 0;
}
- _heap_size = _nb_vertices;
+ heap_size = _nb_vertices;
_source->distance_from_source = 0;
_source->decrease_distance_in_heap(_heap);
- do {
+ while(heap_size > 1) {
// Get the closest to the source
v = _heap[0];
// Remove it from the heap (swap it with the last_slot in the heap, and
// update the distance of that one)
- _heap_size--;
- last_slot = _heap + _heap_size;
+ heap_size--;
+ last_slot = _heap + heap_size;
swap(*_heap, *last_slot); swap((*_heap)->heap_slot, (*last_slot)->heap_slot);
- _heap[0]->increase_distance_in_heap(_heap, _heap + _heap_size);
+ (*_heap)->increase_distance_in_heap(_heap, last_slot);
// Now update the neighbors of the node currently closest to the
// source
d = v->distance_from_source + e->positivized_length;
tv = e->terminal_vertex;
if(d < tv->distance_from_source) {
- ASSERT(tv->heap_slot - _heap < _heap_size);
+ ASSERT(tv->heap_slot < last_slot);
tv->distance_from_source = d;
tv->pred_edge_toward_source = e;
tv->decrease_distance_in_heap(_heap);
}
}
- } while(_heap_size > 0);
+ }
}
void MTPGraph::find_best_paths(scalar_t *lengths) {
//////////////////////////////////////////////////////////////////////
-static int compare_vertices_on_distance(const void *v1, const void *v2) {
- scalar_t delta =
- (*((Vertex **) v1))->distance_from_source -
- (*((Vertex **) v2))->distance_from_source;
- if(delta < 0) return -1;
- else if(delta > 0) return 1;
- else return 0;
-}
-
void MTPGraph::compute_dp_ordering() {
Vertex *v;
Edge *e;
int ntv;
- // This method computes for each node the length of the longest link
- // from the source, and orders the node in _dp_order according to
- // it. It aborts if the graph is not a DAG.
+ // This method orders the nodes by putting first the ones with no
+ // predecessors, then going on adding nodes whose predecessors have
+ // all been already added. Computing the distances from the source
+ // by visiting nodes in that order is equivalent to DP.
int *nb_predecessors = new int[_nb_vertices];
}
}
- scalar_t rank = 1;
while(already_processed < front) {
new_front = front;
while(already_processed < front) {
v = *(already_processed++);
- v->distance_from_source = rank;
for(e = v->leaving_edge_list_root; e; e = e->next_leaving_edge) {
ntv = int(e->terminal_vertex - _vertices);
nb_predecessors[ntv]--;
}
}
front = new_front;
- rank++;
}
if(already_processed < _dp_order + _nb_vertices) {
}
delete[] nb_predecessors;
-
- for(int v = 0; v < _nb_vertices; v++) { _dp_order[v] = &_vertices[v]; }
- qsort(_dp_order, _nb_vertices, sizeof(Vertex *), compare_vertices_on_distance);
}
//////////////////////////////////////////////////////////////////////