void
pq_delete_min(PQ pq, void *retval)
{
int floater; /* previous loser floating down */
int small_child; /* smaller child of floater */
assert(!pq_is_empty(pq));
/* first copy out the winner */
memcpy(retval, REF(pq, 0), pq->element_length);
--(pq->n);
if(pq_is_empty(pq)) {
/* pq empty, nothing to do */
return;
}
/* else */
memcpy(REF(pq, 0), REF(pq, pq->n), pq->element_length);
floater = 0;
for(;;) {
/* find smaller child of floater */
if(Child(floater, 0) >= pq->n) {
return; /* no children, bail out */
} else if(Child(floater, 1) >= pq->n) {
small_child = Child(floater, 0);
} else if(pq->compare(REF(pq, Child(floater, 0)), REF(pq, Child(floater, 1))) < 0) {
small_child = Child(floater, 0);
} else {
small_child = Child(floater, 1);
}
/* is floater <= small_child? */
if(pq->compare(REF(pq, floater), REF(pq, small_child)) <= 0) {
/* yes, we are done */
return;
} else {
/* no, swap and continue floating down */
pq_swap(pq, floater, small_child);
floater = small_child;
}
}
}
void
pq_sanity_check(PQ pq)
{
int i;
int j;
assert(pq->n >= 0);
assert(pq->n <= pq->size);
for(i = 0; i < pq->n; i++) {
for(j = 0; j < NUM_CHILDREN; j++) {
if(Child(i, j) < pq->n) {
assert(pq->compare(REF(pq, i), REF(pq, Child(i, j))) <= 0);
}
}
}
}
void
pq_insert(PQ pq, const void *elt)
{
int floater; /* new element */
while(pq->n + 1 > pq->size) {
pq->size *= 2;
pq->data = realloc(pq->data, pq->element_length * pq->size);
assert(pq->data);
}
/* copy the new element in */
floater = pq->n++;
memcpy(REF(pq, floater), elt, pq->element_length);
/* float it up until it is at the top */
/* or it is no smaller than its parent */
while(floater > 0 && pq->compare(REF(pq, floater), REF(pq, Parent(floater))) <= 0) {
/* it's smaller than its parent */
pq_swap(pq, floater, Parent(floater));
floater = Parent(floater);
}
}
