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indexing
	description: "Binary tree: each node may have a left child and a right child"
	status: "See notice at end of class"
	names: binary_tree, tree, fixed_tree
	representation: recursive, array
	access: cursor, membership
	contents: generic
	date: "$Date: 2001/11/16 20:34:24 $"
	revision: "$Revision: 1.1.1.1 $"

class 
	BINARY_TREE [G]

create 
	make

feature -- Initialization

	make (v: like item) is
			-- Create a root node with value v.
		do
			item := v
		ensure
			is_root: is_root
			is_leaf: is_leaf
		end
	
feature -- Access

	child: like parent is
			-- Child at cursor position
		require -- from TREE
			readable: readable_child
		do
			inspect child_index
			when 1 then 
				Result := left_child
			when 2 then 
				Result := right_child
			end
		end

	child_cursor: CURSOR is
			-- Current cursor position
		do
			create {ARRAYED_LIST_CURSOR} Result.make (child_index)
		end

	child_index: INTEGER
			-- Index of cursor position

	child_item: like item is
			-- Item in current child node
			-- (from TREE)
		require -- from TREE
			readable: child_readable
		do
			Result := child.item
		end

	first_child: like parent is
			-- Left child
		require -- from TREE
			is_not_leaf: not is_leaf
		do
			Result := left_child
		end

	item: G
			-- Content of cell.
			-- (from CELL)

	last_child: like parent is
			-- Right child
		require -- from TREE
			is_not_leaf: not is_leaf
		do
			Result := right_child
		end

	left_child: like parent
			-- Left child, if any

	left_item: like item is
			-- Value of left child
		require
			has_left: left_child /= void
		do
			Result := left_child.item
		end

	left_sibling: like parent is
			-- Left neighbor, if any
		require -- from TREE
			is_not_root: not is_root
		do
			if parent.right_child = Current then
				Result := parent.left_child
			end
		ensure -- from TREE
			is_sibling: Result /= void implies is_sibling (Result)
			right_is_current: (Result /= void) implies (Result.right_sibling = Current)
		end

	parent: BINARY_TREE [G]
			-- Parent of current node

	right_child: like parent
			-- Right child, if any

	right_item: like item is
			-- Value of right child
		require
			has_right: right_child /= void
		do
			Result := right_child.item
		end

	right_sibling: like parent is
			-- Right neighbor, if any
		require -- from TREE
			is_not_root: not is_root
		do
			if parent.left_child = Current then
				Result := parent.right_child
			end
		ensure -- from TREE
			is_sibling: Result /= void implies is_sibling (Result)
			left_is_current: (Result /= void) implies (Result.left_sibling = Current)
		end
	
feature -- Measurement

	arity: INTEGER is
			-- Number of children
		do
			if has_left then
				Result := Result + 1
			end
			if has_right then
				Result := Result + 1
			end
		ensure then
			valid_arity: Result <= 2
		end

	count: INTEGER is
			-- Number of items
			-- (from TREE)
		do
			Result := subtree_count + 1
		end
	
feature -- Comparison

	is_equal (other: like Current): BOOLEAN is
			-- Does other contain the same elements?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from TREE)
		require -- from ANY
			other_not_void: other /= void
		do
			if Current = other then
				Result := True
			else
				Result := (is_empty = other.is_empty) and (object_comparison = other.object_comparison) and (child_capacity = other.child_capacity)
				if Result and not is_empty then
					Result := tree_is_equal (Current, other)
				end
			end
		ensure -- from ANY
			symmetric: Result implies other.is_equal (Current)
			consistent: standard_is_equal (other) implies Result
		end
	
feature -- Status report

	changeable_comparison_criterion: BOOLEAN is
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)
		do
			Result := True
		end

	child_after: BOOLEAN is
			-- Is there no valid child position to the right of cursor?
		do
			Result := child_index >= child_capacity + 1
		end

	child_before: BOOLEAN is
			-- Is there no valid child position to the left of cursor?
			-- (from TREE)
		do
			Result := child_index = 0
		end

	child_isfirst: BOOLEAN is
			-- Is cursor under first child?
			-- (from TREE)
		do
			Result := not is_leaf and child_index = 1
		ensure -- from TREE
			not_is_leaf: Result implies not is_leaf
		end

	child_islast: BOOLEAN is
			-- Is cursor under last child?
			-- (from TREE)
		do
			Result := not is_leaf and child_index = child_capacity
		ensure -- from TREE
			not_is_leaf: Result implies not is_leaf
		end

	child_off: BOOLEAN is
			-- Is there no current child?
			-- (from TREE)
		do
			Result := child_before or child_after
		end

	child_readable: BOOLEAN is
			-- Is there a current child_item to be read?
			-- (from TREE)
		do
			Result := not child_off and then (child /= void)
		end

	child_writable: BOOLEAN is
			-- Is there a current child_item that may be modified?
			-- (from TREE)
		do
			Result := not child_off and then (child /= void)
		end

	empty: BOOLEAN is
		obsolete "ELKS 2000: Use `is_empty' instead"
			-- Is there no element?
			-- (from CONTAINER)
		do
			Result := is_empty
		end

	has (v: G): BOOLEAN is
			-- Does subtree include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from TREE)
		do
			if object_comparison then
				Result := (v /= void) and then (item /= void) and then (v.is_equal (item) or else subtree_has (v))
			else
				Result := v = item or else subtree_has (v)
			end
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		end

	has_both: BOOLEAN is
			-- Has current node two children?
		do
			Result := left_child /= void and right_child /= void
		ensure
			Result = (has_left and has_right)
		end

	has_left: BOOLEAN is
			-- Has current node a left child?
		do
			Result := left_child /= void
		ensure
			Result = (left_child /= void)
		end

	has_none: BOOLEAN is
			-- Are there no children?
			-- Was declared in BINARY_TREE as synonym of is_leaf.
		do
			Result := left_child = void and right_child = void
		end

	has_right: BOOLEAN is
			-- Has current node a right child?
		do
			Result := right_child /= void
		ensure
			Result = (right_child /= void)
		end

	is_empty: BOOLEAN is
			-- Is structure empty of items?
			-- (from TREE)
		do
			Result := False
		end

	is_leaf: BOOLEAN is
			-- Are there no children?
			-- Was declared in BINARY_TREE as synonym of has_none.
		do
			Result := left_child = void and right_child = void
		end

	is_root: BOOLEAN is
			-- Is there no parent?
			-- (from TREE)
		do
			Result := parent = void
		end

	is_sibling (other: like parent): BOOLEAN is
			-- Are current node and other siblings?
			-- (from TREE)
		require -- from TREE
			other_exists: other /= void
		do
			Result := not is_root and other.parent = parent
		ensure -- from TREE
			not_root: Result implies not is_root
			other_not_root: Result implies not other.is_root
			same_parent: Result = not is_root and other.parent = parent
		end

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	Readable: BOOLEAN is True
			-- (from TREE)

	readable_child: BOOLEAN is
			-- Is there a current child to be read?
			-- (from TREE)
		do
			Result := not child_off
		end

	valid_cursor_index (i: INTEGER): BOOLEAN is
			-- Is i correctly bounded for cursor movement?
			-- (from TREE)
		do
			Result := (i >= 0) and (i <= child_capacity + 1)
		ensure -- from TREE
			valid_cursor_index_definition: Result = (i >= 0) and (i <= child_capacity + 1)
		end

	Writable: BOOLEAN is True
			-- Is there a current item that may be modified?
			-- (from TREE)

	writable_child: BOOLEAN is
			-- Is there a current child that may be modified?
			-- (from TREE)
		do
			Result := not child_off
		end
	
feature -- Status setting

	compare_objects is
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		do
			object_comparison := True
		ensure -- from CONTAINER
			object_comparison
		end

	compare_references is
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		do
			object_comparison := False
		ensure -- from CONTAINER
			reference_comparison: not object_comparison
		end
	
feature -- Cursor movement

	child_back is
			-- Move cursor to previous child.
		do
			child_index := child_index - 1
		end

	child_finish is
			-- Move cursor to last child.
		do
			child_index := 2
		ensure then -- from TREE
			is_last_child: not is_leaf implies child_islast
		end

	child_forth is
			-- Move cursor to next child.
		do
			child_index := child_index + 1
		end

	child_go_i_th (i: INTEGER) is
			-- Move cursor to i-th child.
		require else -- from TREE
			valid_cursor_index: valid_cursor_index (i)
		do
			child_index := i
		ensure then -- from TREE
			position: child_index = i
		end

	child_go_to (p: ARRAYED_LIST_CURSOR) is
			-- Move cursor to child remembered by p.
		do
			child_index := p.index
		end

	child_start is
			-- Move to first child.
		do
			child_index := 1
		ensure then -- from TREE
			is_first_child: not is_leaf implies child_isfirst
		end
	
feature -- Element change

	child_put (v: like item) is
			-- Put v at current child position.
			-- Was declared in BINARY_TREE as synonym of child_replace.
		require -- from TREE
			child_writable: child_writable
		local
			node: like Current
		do
			if child /= void then
				if object_comparison then
					child.compare_objects
				else
					child.compare_references
				end
				child.put (v)
			else
				create node.make (v)
				if object_comparison then
					node.compare_objects
				end
				put_child (node)
			end
		ensure -- from TREE
			item_inserted: child_item = v
		end

	child_replace (v: like item) is
			-- Put v at current child position.
			-- Was declared in BINARY_TREE as synonym of child_put.
		require -- from TREE
			child_writable: child_writable
		local
			node: like Current
		do
			if child /= void then
				if object_comparison then
					child.compare_objects
				else
					child.compare_references
				end
				child.put (v)
			else
				create node.make (v)
				if object_comparison then
					node.compare_objects
				end
				put_child (node)
			end
		ensure -- from TREE
			item_inserted: child_item = v
		end

	fill (other: TREE [G]) is
			-- Fill with as many items of other as possible.
			-- The representations of other and current node
			-- need not be the same.
			-- (from TREE)
		do
			replace (other.item)
			fill_subtree (other)
		end

	put (v: like item) is
			-- Make v the cell's item.
			-- Was declared in CELL as synonym of replace.
			-- (from CELL)
		require -- from TREE
			is_writable: writable
		do
			item := v
		ensure -- from TREE
			item_inserted: item = v
		ensure -- from CELL
			item_inserted: item = v
		end

	put_child (n: like parent) is
			-- Put n at current child position.
			-- Was declared in BINARY_TREE as synonym of replace_child.
		do
			if object_comparison then
				n.compare_objects
			else
				n.compare_references
			end
			n.attach_to_parent (Current)
			inspect child_index
			when 1 then 
				left_child := n
			when 2 then 
				right_child := n
			end
		end

	put_left_child (n: like parent) is
			-- Set left_child to n.
		require
			no_parent: n = void or else n.is_root
		do
			if n /= void then
				if object_comparison then
					n.compare_objects
				else
					n.compare_references
				end
			end
			if left_child /= void then
				left_child.attach_to_parent (void)
			end
			if n /= void then
				n.attach_to_parent (Current)
			end
			left_child := n
		end

	put_right_child (n: like parent) is
			-- Set right_child to n.
		require
			no_parent: n = void or else n.is_root
		do
			if n /= void then
				if object_comparison then
					n.compare_objects
				else
					n.compare_references
				end
			end
			if right_child /= void then
				right_child.attach_to_parent (void)
			end
			if n /= void then
				n.attach_to_parent (Current)
			end
			right_child := n
		end

	replace (v: like item) is
			-- Make v the cell's item.
			-- Was declared in CELL as synonym of put.
			-- (from CELL)
		require -- from TREE
			is_writable: writable
		do
			item := v
		ensure -- from TREE
			item_inserted: item = v
		ensure -- from CELL
			item_inserted: item = v
		end

	replace_child (n: like parent) is
			-- Put n at current child position.
			-- Was declared in BINARY_TREE as synonym of put_child.
		require -- from TREE
			writable_child: writable_child
			was_root: n.is_root
		do
			if object_comparison then
				n.compare_objects
			else
				n.compare_references
			end
			n.attach_to_parent (Current)
			inspect child_index
			when 1 then 
				left_child := n
			when 2 then 
				right_child := n
			end
		ensure -- from TREE
			child_replaced: child = n
		end

	sprout is
			-- Make current node a root.
			-- (from TREE)
		do
			if parent /= void then
				parent.prune (Current)
			end
		end
	
feature -- Removal

	child_remove is
			-- Remove current child.
		do
			inspect child_index
			when 1 then 
				left_child.attach_to_parent (void);
				left_child := void
			when 2 then 
				right_child.attach_to_parent (void);
				right_child := void
			end
		end

	prune (n: like parent) is
			-- Prune n from child nodes.
		require -- from TREE
			is_child: n.parent = Current
		do
			if left_child = n then
				remove_left_child
			elseif right_child = n then
				remove_right_child
			end
		ensure -- from TREE
			n_is_root: n.is_root
		end

	remove_left_child is
			-- Remove left child.
		do
			if left_child /= void then
				left_child.attach_to_parent (void)
			end
			left_child := void
		ensure
			not has_left
		end

	remove_right_child is
			-- Remove right child.
		do
			if right_child /= void then
				right_child.attach_to_parent (void)
			end
			right_child := void
		ensure
			not has_right
		end
	
feature -- Conversion

	binary_representation: BINARY_TREE [G] is
			-- Convert to binary tree representation:
			-- first child becomes left child,
			-- right sibling becomes right child.
			-- (from TREE)
		local
			current_sibling: BINARY_TREE [G]
		do
			create Result.make (item)
			if not is_leaf then
				Result.put_left_child (first_child.binary_representation)
				from
					child_start
					child_forth
					current_sibling := Result.left_child
				until
					child_after
				loop
					current_sibling.put_right_child (child.binary_representation)
					current_sibling := current_sibling.right_child
					child_forth
				end
			end
		ensure -- from TREE
			result_is_root: Result.is_root
			result_has_no_right_child: not Result.has_right
		end

	linear_representation: LINEAR [G] is
			-- Representation as a linear structure
			-- (from TREE)
		local
			al: ARRAYED_LIST [G]
		do
			create al.make (count)
			al.start
			al.extend (item)
			fill_list (al)
			Result := al
		end
	
feature -- Duplication

	copy (other: like Current) is
			-- Copy contents from other.
		require -- from ANY
			other_not_void: other /= void
			type_identity: same_type (other)
		local
			tmp_tree: like Current
		do
			create tmp_tree.make (other.item)
			if not other.is_leaf then
				tree_copy (other, tmp_tree)
			end
		ensure -- from ANY
			is_equal: is_equal (other)
		end

	duplicate (n: INTEGER): like Current is
			-- Copy of sub-tree beginning at cursor position and
			-- having min (n, arity - child_index + 1)
			-- children.
		require -- from TREE
			not_child_off: not child_off
			valid_sublist: n >= 0
		do
			Result := new_tree
			if child_index <= 1 and child_index + n >= 1 and has_left then
				Result.put_left_child (left_child.duplicate_all)
			end
			if child_index <= 2 and child_index + n >= 2 and has_right then
				Result.put_right_child (right_child.duplicate_all)
			end
		end

	duplicate_all: like Current is
		do
			Result := new_tree
			if has_left then
				Result.put_left_child (left_child.duplicate_all)
			end
			if has_right then
				Result.put_right_child (right_child.duplicate_all)
			end
		end
	
feature {BINARY_TREE} -- Implementation

	fill_list (al: ARRAYED_LIST [G]) is
			-- Fill al with all the children's items.
		do
			if left_child /= void then
				al.extend (left_child.item)
				left_child.fill_list (al)
			end
			if right_child /= void then
				al.extend (right_child.item)
				right_child.