fib_heap.pl : Fibonacci heap priority queue Optimal Fibonacci heap implementation based on [Fredman & Tarjan, J. ACM 34(3), 1987]. Maintain a priority queue which contains item-priority pairs. Items are integers > 0, priorities are any numeric type. An item-priority pair can be added, its priority can be decreased, and the item with the lowest priority can be extracted (find+remove).
How to use: The following operations are supported: insert(I,P): add item I with priority P extract_min(I,P): returns minimal priority pair I-P and removes it decr(I,NP): decreases the priority of I to the new value NP (only if NP is smaller than the old priority) decr_or_ins(I,P): decreases the priority of I, or inserts it if it is not in the queue Data is represented internally as: item(I,P,Rank,Parent,Mark): a node in the Fibonacci heap. Parent=0 for roots. See literature for Rank and Mark. min(I,P): current minimal element Internal operations are: findmin: [extract_min] find the new minimal element ch2rt(I): [extract_min] convert the children of I to roots decr(I,NP,R,P,M): [decr] re-inserts an item in a decrease operation, respecting heap order mark(I): [decr] mark I, and if necessary, cut it off and mark its parent
See also: Fibonacci heaps are used in dijkstra.pl Reference paper: Dijkstra's Algorithm with Fibonacci Heaps: An Executable Description in CHR. Jon Sneyers, Tom Schrijvers and Bart Demoen. WLP 2006.
Program: Change the code, then submit! /* fib_heap.pl: Fibonacci heap priority queue (C) Jon.Sneyers at cs.kuleuven.be, 2006 This program is distributed under the terms of the GNU General Public License: http://www.gnu.org/licenses/gpl.html %% DESCRIPTION Optimal Fibonacci heap implementation based on [Fredman & Tarjan, J. ACM 34(3), 1987]. Maintain a priority queue which contains item-priority pairs. # Items are integers > 0, priorities are any numeric type. An item-priority pair can be added, its priority can be decreased, and the item with the lowest priority can be extracted (find+remove). %% HOW TO USE The following operations are supported: # *insert(I,P)*: add item I with priority P # *extract_min(I,P)*: returns minimal priority pair I-P and removes it # *decr(I,NP)*: decreases the priority of I to the new value NP (only if NP is smaller than the old priority) # *decr_or_ins(I,P)*: decreases the priority of I, or inserts it if it is not in the queue Data is represented internally as: # *item(I,P,Rank,Parent,Mark)*: a node in the Fibonacci heap. Parent=0 for roots. See literature for Rank and Mark. # *min(I,P)*: current minimal element Internal operations are: # *findmin*: [extract_min] find the new minimal element # *ch2rt(I)*: [extract_min] convert the children of I to roots # *decr(I,NP,R,P,M)*: [decr] re-inserts an item in a decrease operation, respecting heap order # *mark(I)*: [decr] mark I, and if necessary, cut it off and mark its parent %% SEE ALSO Fibonacci heaps are used in dijkstra.pl# Reference paper: Dijkstra's Algorithm with Fibonacci Heaps: An Executable Description in CHR. Jon Sneyers, Tom Schrijvers and Bart Demoen. WLP 2006. %% SAMPLE QUERIES Q: insert(1,8), insert(2,4), insert(3,6), decr(1,5), extract_min(A1,A2), extract_min(B1,B2), extract_min(C1,C2). A: A1 = 2, A2 = 4, B1 = 1, B2 = 5, C1 = 3, C2 = 6. */ :- module(fib_heap, [insert/2, extract_min/2, decr/2, decr_or_ins/2]). :- use_module(library(chr)). %% Deprecated syntax used for SICStus 3.x %handler fib. %constraints % insert/2, % extract_min/2, % decr/2, % decr_or_ins/2, % % internal: % item/5, % min/2, % decr/5, % mark/1, % ch2rt/1, % findmin/0. %% Syntax for SWI / SICStus 4.x :- chr_constraint insert(+int,+number), extract_min(?int,?number), decr(+int,+number), decr_or_ins(+int,+number), % internal: item(+node,+number,+int,+node,?mark), min(+int,+number), decr(+int,+number,+int,+int,+mark), mark(+int), ch2rt(+int), findmin. :- chr_type mark ---> m ; u. %:- chr_type node == dense_int. % efficient: arrays :- chr_type node == int. % less efficient: hashtables insert @ insert(I,K) <=> item(I,K,0,0,u), min(I,K). keep_min @ min(_,A) \ min(_,B) <=> A =< B | true. extr @ extract_min(X,Y), min(I,K), item(I,_,_,_,_) <=> ch2rt(I), findmin, X=I, Y=K. extr_empty @ extract_min(_,_) <=> fail. c2r @ ch2rt(I) \ item(C,K,R,I,_)#X <=> item(C,K,R,0,u) pragma passive(X). c2r_done @ ch2rt(_) <=> true. findmin @ findmin, item(I,K,_,0,_) ==> min(I,K). foundmin @ findmin <=> true. same_rank @ item(I1,K1,R,0,_), item(I2,K2,R,0,_) <=> R1 is R+1, (K1 < K2 -> item(I2,K2,R,I1,u), item(I1,K1,R1,0,u) ; item(I1,K1,R,I2,u), item(I2,K2,R1,0,u)). decr @ decr(I,K), item(I,O,R,P,M) <=> K < O | decr(I,K,R,P,M). decr_nok @ decr(_,_) <=> fail. doi-decr @ item(I,O,R,P,M), decr_or_ins(I,K) <=> K < O | decr(I,K,R,P,M). doi-nop @ item(I,O,_,_,_) \ decr_or_ins(I,K) <=> K >= O | true. doi-insert @ decr_or_ins(I,K) <=> insert(I,K). d_min @ decr(I,K,_,_,_) ==> min(I,K). d_root @ decr(I,K,R,0,_) <=> item(I,K,R,0,u). d_noprob @ item(P,PK,_,_,_) \ decr(I,K,R,P,M) <=> K >= PK | item(I,K,R,P,M). d_prob @ decr(I,K,R,P,_) <=> item(I,K,R,0,u), mark(P). m_rt @ mark(I), item(I,K,R,P,_) <=> P=0 | R1 is R-1, item(I,K,R1,0,u). m_m @ mark(I), item(I,K,R,P,M) <=> M=m | R1 is R-1, item(I,K,R1,0,u),mark(P). m_u @ mark(I), item(I,K,R,P,M) <=> M=u | R1 is R-1, item(I,K,R1,P,m). m_er @ mark(_) <=> writeln(error_mark), fail.
Console: Enter query or select example from below, then submit and wait for answer! % loading graph/fib_heap.pl | ?- consult(...). yes [0.422 seconds] | ?-