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Note Description Vertex Item Generic Parameter Well Incoming Outgoing Edges Item G Outgoin Q43868018

note
description: “[
A vertex has an item in the generic parameter,
as well as incoming and outgoing edges:
item: G
outgoing: LIST[EDGE[G]]
incoming: LIST[EDGE[G]]
outgoing_sorted: ARRAY[EDGE[G]]
outgoing_sorted is an array of edges
sorted based on comparable items in destination vertices. Thisallows
for a unique ordering as in breadth first searches etc.
]”
note_to_student: “[
Only modify features that have a `Todo` comment inside ofthem.
You must also write the postcondition for command`remove_edge`.

]”

class
VERTEX[G -> COMPARABLE]
inherit
ANY
redefine is_equal, out end

DEBUG_OUTPUT
redefine is_equal, out end

COMPARABLE
redefine is_equal, out end
create
make

feature {NONE} — Initialization

make(a_item: G)
— Initialization for `Current’.
do
create {LINKED_LIST[EDGE[G]]}outgoing.make
outgoing.compare_objects
create {LINKED_LIST[EDGE[G]]}incoming.make
incoming.compare_objects
item := a_item
ensure
item_set:
item ~ a_item
empty_edges:
outgoing.is_empty and incoming.is_empty
end

feature — Comparable

is_less alias “<” (other: like Current): BOOLEAN
— Is current object less than `other’?
do
Result := item < other.item
end

is_equal(other: like Current): BOOLEAN
do
Result := item ~ other.item
end

feature — basic queries
item: G

outgoing: LIST[EDGE[G]]
— outging edges

incoming: LIST[EDGE[G]]
— incoming edges

feature — derived queries

outgoing_sorted: ARRAY[EDGE[G]]
— Return outgoing edges as a sorted array
— (based on destination vertices of edges).
do

— Todo: complete implementation

create Result.make_empty — this line is for compilationpurposes
ensure
— ∀ i ∈ 1 .. (Result.count – 1) : Result[i].destination ≤ Result[i+ 1].destination
sorted:
across 1 |..| (Result.count – 1) as l_i all
Result[l_i.item].destination <= Result[l_i.item +1].destination
end
end

outgoing_edge_count: INTEGER
— number of outgoing edges
do

— Todo: complete implementation

ensure
outgoing_edge_count:
Result = outgoing.count
end

incoming_edge_count: INTEGER
— number of incoming edges
do

— Todo: complete implementation

ensure
incoming_edge_count:
Result = incoming.count
end

edge_count: INTEGER
— number of incoming and outgoing edges
do

— Todo: complete implementation

ensure
correct_count:
Result = incoming_edge_count + outgoing_edge_count
end

has_outgoing_edge(a_edge: EDGE[G]): BOOLEAN
— `Current` has `a_edge` as an outgoing edge
do

— Todo: complete implementation

ensure
Result = outgoing.has (a_edge)
end

has_incoming_edge(a_edge: EDGE[G]): BOOLEAN
— `Current` has `a_edge` as an incoming edge
do

— Todo: complete implementation

ensure
Result = incoming.has (a_edge)
end

feature — commands

add_edge(a_edge: EDGE[G])
require
edge_contains_current: a_edge.source ~ Current ora_edge.destination ~ Current
new_edge: not (has_incoming_edge (a_edge) or has_outgoing_edge(a_edge))
do

— Todo: complete implementation

ensure
a_edge.destination ~ Current implies incoming.count = oldincoming.count + 1
a_edge.source ~ Current implies outgoing.count = old outgoing.count+ 1
a_edge.destination ~ Current implies incoming.has (a_edge)
a_edge.source ~ Current implies outgoing.has (a_edge)
— incomplete, to add!
end

remove_edge(a_edge: EDGE[G])
require
a_edge.source ~ Current or a_edge.destination ~ Current
do

— Todo: complete implementation

ensure
— To do.
end

feature — out

out: STRING
— Return string representation of current vertex
do
Result := item.out + “:”
across outgoing_sorted as l_edge loop
Result := Result + l_edge.item.debug_output +”,”
end
Result.remove (Result.count)
end

debug_output: STRING
— Return string representation of current vertex in debugger
do
Result := item.out + “:”
across outgoing_sorted as l_edge loop
Result := Result + l_edge.item.destination.item.out +”,”
end
Result.remove (Result.count)
end

invariant
outgoing_edges_start_with_current:
across outgoing as l_edge all
l_edge.item.source ~ Current
end

incoming_edges_end_with_current:
across incoming as l_edge all
l_edge.item.destination ~ Current
end

object_comparison:
outgoing.object_comparison and incoming.object_comparison
end

Expert Answer

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Answer to note description: “[ A vertex has an item in the generic parameter, as well as incoming and outgoing edges: item: G outg…