13.3 Insertion

The only difference between this code and <BST item insertion function 33> is that we set n's parent pointer after insertion.

492. <PBST item insertion function 492> =
void **
pbst_probe (struct pbst_table *tree, void *item) 
{
  struct pbst_node *p, *q; /* Current node in search and its parent. */
  int dir;                 /* Side of q on which p is located. */
  struct pbst_node *n;     /* Newly inserted node. */

  assert (tree != NULL && item != NULL);

  <Step 1: Search PBST tree for insertion point 493>
  <Step 2: Insert PBST node 494>

  return &n->pbst_data;
}

This code is included in 491.

493. <Step 1: Search PBST tree for insertion point 493> =
for (q = NULL, p = tree->pbst_root; p != NULL; q = p, p = p->pbst_link[dir]) 
  {
    int cmp = tree->pbst_compare (item, p->pbst_data, tree->pbst_param);
    if (cmp == 0)
      return &p->pbst_data;
    dir = cmp > 0;
  }

This code is included in 492 and 557.

494. <Step 2: Insert PBST node 494> =
n = tree->pbst_alloc->libavl_malloc (tree->pbst_alloc, sizeof *p);
if (n == NULL)
  return NULL;

tree->pbst_count++;
n->pbst_link[0] = n->pbst_link[1] = NULL;
n->pbst_parent = q;
n->pbst_data = item;
if (q != NULL)
  q->pbst_link[dir] = n;
else 
  tree->pbst_root = n;

This code is included in 492, 527, and 558.

See also:  [Cormen 1990], section 13.3.