/tutorial/backtracking/logigram/constraint_set.e

  1-- See the Copyright notice at the end of this file.
  2--
  3class CONSTRAINT_SET
  4	--
  5	-- the set of constraints
  6	--
  7
  8creation {ANY}
  9	make
 10
 11feature {ANY}
 12	groups: LINKED_LIST[CONSTRAINT_GROUP]
 13			-- the constraints that contains variable items
 14			-- where constraints are grouped around coupled variables 
 15
 16	unbound: CONSTRAINT_GROUP
 17			-- the constarints that are not bound to any variable
 18
 19	make is
 20			-- creation
 21		do
 22			create groups.make
 23			create unbound.make
 24			create collector.make
 25		end
 26
 27	add (constraint: CONSTRAINT) is
 28			-- add a constraint, taking care of where it must go:
 29			-- either in the unbound group or in one of the groups
 30			-- bound to variables
 31		local
 32			i: INTEGER; grp: CONSTRAINT_GROUP; added: BOOLEAN
 33		do
 34			-- Collects the items
 35			collector.clear
 36			constraint.get_items(collector)
 37			if collector.has_var then
 38				-- There is a variable.
 39				from
 40					i := groups.lower
 41				until
 42					i > groups.upper
 43				loop
 44					grp := groups.item(i)
 45					if not grp.var_set.is_disjoint_from(collector.var_set) then
 46						-- grp is the first group that contains one of the 
 47						-- variables of the constraint.
 48						-- Add the constraint to the group
 49						grp.add(constraint, collector.var_set)
 50						added := True
 51						i := i + 1
 52						-- Checks is further groups intersect the new one.
 53						from
 54						until
 55							i > groups.upper
 56						loop
 57							if grp.var_set.is_disjoint_from(groups.item(i).var_set) then
 58								i := i + 1
 59							else
 60								-- Merge of the two intersecting groups
 61								grp.union(groups.item(i))
 62								groups.remove(i)
 63							end
 64						end
 65						check
 66							i > groups.upper -- obvious, the main loop stops
 67						end
 68					else
 69						i := i + 1
 70					end
 71				end
 72				if not added then
 73					-- When not added, the constraint begins a new group.
 74					create grp.make
 75					grp.add(constraint, collector.var_set)
 76					groups.add_last(grp)
 77				end
 78			else
 79				-- No variables, adds to the unbound group of constraints.
 80				unbound.add(constraint, collector.var_set)
 81			end
 82		end
 83
 84	build_nodes (builder: MASK_BUILDER): BACKTRACKING_NODE_AND_LIST is
 85			-- Creates the backtracking tree corresponding to the constraints.
 86		local
 87			i: INTEGER; n: BACKTRACKING_NODE
 88		do
 89			-- The creation begins with variable groups.
 90			from
 91				i := groups.lower
 92			until
 93				i > groups.upper
 94			loop
 95				n := groups.item(i).build_nodes(builder)
 96				if n /= Void then
 97					Result := create {BACKTRACKING_NODE_AND_LIST}.make(n, Result)
 98				end
 99				i := i + 1
100			end
101			-- Creation of the not variable group.
102			-- Note: made after to go before in the list.
103			n := unbound.build_nodes(builder)
104			if n /= Void then
105				Result := create {BACKTRACKING_NODE_AND_LIST}.make(n, Result)
106			end
107		end
108
109	collector: ITEM_COLLECTOR
110		-- common collector of items
111
112end -- class CONSTRAINT_SET
113--
114-- ------------------------------------------------------------------------------------------------------------------------------
115-- Copyright notice below. Please read.
116--
117-- This file is free software, which comes along with SmartEiffel. This software is distributed in the hope that it will be
118-- useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
119-- You can modify it as you want, provided this footer is kept unaltered, and a notification of the changes is added.
120-- You are allowed to redistribute it and sell it, alone or as a part of another product.
121--
122-- Copyright(C) 1994-2002: INRIA - LORIA (INRIA Lorraine) - ESIAL U.H.P.       - University of Nancy 1 - FRANCE
123-- Copyright(C) 2003-2005: INRIA - LORIA (INRIA Lorraine) - I.U.T. Charlemagne - University of Nancy 2 - FRANCE
124--
125-- Authors: Dominique COLNET, Philippe RIBET, Cyril ADRIAN, Vincent CROIZIER, Frederic MERIZEN
126--
127-- http://SmartEiffel.loria.fr - SmartEiffel@loria.fr
128-- ------------------------------------------------------------------------------------------------------------------------------