Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

waiting list. Thus, we would like to remove from the priority queue the entry
associated with this passenger. Operation removeMin is not suitable for this
purpose since the passenger leaving is unlikely to have first priority. Instead, we
would like to have a new operation remove (e) that removes an arbitrary entry e.
• Another standby passenger finds her gold frequent-flyer card and shows it to the
agent. Thus, her priority has to be modified accordingly. To achieve this change of
priority, we would like to have a new operation replaceKey(e,k) that replaces
with k the key of entry e in the priority queue.
• Finally, a third standby passenger notices her name is misspelled on the ticket and
asks it to be corrected. To perform the change, we need to up date the passenger's
record. Hence, we would like to have a new operation replaceValue(e,x) that
replaces with x the value of entry e in the priority queue.
8.4.1 Methods of the Adaptable Priority Queue ADT
The above scenarios motivate the definition of a new ADT that extends the prior ity
queue ADT with methods remove, replaceKey, and replaceValue.
Namely, an adaptable priority queue P supports the following methods in addition
to those of the priority queue ADT:
remove(e): Remove from P and return entry e.
replaceKey(e,k): Replace with k and return the key of entry e of P; an
be
error condition occurs if k is invalid (that is, k cannot
compared with other keys).
replaceValue(e,x): Replace with x and return the value of entry e of P.
Example 8.8: The following table shows a series of operations and their effects
on an initially empty adaptable priority queue P.
Operation
Output
P
insert(5,A)
e 1
{(5,A)}
496