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Option Explicit On
Option Strict   On
Option Compare  Binary
Option Infer    On
 
Imports System.Collections.Generic
Imports System.Numerics
Imports Tp = System.Tuple(Of Integer, Integer)
 
Public Class CheckPolygon
	Private Class Point
		Public ReadOnly x, y As BigInteger
		Sub New (x As Integer, y As Integer)
			Me.x = x: Me.y = y
		End Sub
		Function Gaiseki(p1 As Point, p2 As Point) As BigInteger
			Dim a As BigInteger = (p1.x - Me.x) * (p2.y - Me.y)
			Dim b As BigInteger = (p1.y - Me.y) * (p2.x - Me.x)
			Gaiseki = a - b
		End Function
	End Class
	Private Class Line
		Public ReadOnly p1, p2 As Point
		Public ReadOnly dx, dy As BigInteger
		Sub New (p1 As Point, p2 As Point)
			Me.p1 = p1: Me.p2 = p2
			Me.dx = p2.x - p1.x
			Me.dy = p2.y - p1.y
		End Sub
		Function IsPara(other As Line) As Boolean
			If Me.dx = 0 Then
				IsPara = other.dx = 0
			ElseIf other.dx = 0 Then
				IsPara = Me.dx = 0
			ElseIf Me.dy = 0 Then
				IsPara = other.dy = 0
			ElseIf other.dy = 0 Then
				IsPara = Me.dy = 0
			Else
				Dim a As BigInteger = Me.dx * other.dy
				Dim b As BigInteger = Me.dy * other.dx
				IsPara = a - b = 0
			End If
		End Function
		Function IsIntersect(other As Line) As Boolean
			IsIntersect = False
			If IsPara(other) Then Exit Function
			Dim a As BigInteger = Me.p1.Gaiseki(Me.p2, other.p1)
			Dim b As BigInteger = Me.p1.Gaiseki(Me.p2, other.p2)
			Dim c As BigInteger = other.p1.Gaiseki(other.p2, Me.p1)
			Dim d As BigInteger = other.p1.Gaiseki(other.p2, Me.p2)
			IsIntersect = a * b <= 0 AndAlso c * d <= 0
		End Function
	End Class
	Public Function check(X As Integer(), Y As Integer()) As String
		check = "Not simple"
		Dim N As Integer = X.Length
		Dim lines(N) As Line
		Dim hs As New HashSet(Of Tp)()
		For i As Integer = 0 To N - 1
			Dim t As New Tp(X(i), Y(i))
			If Not hs.Add(t) Then Exit Function
		Next i
		For i As Integer = 0 To N - 2
			Dim p1 As New Point(X(i), Y(i))
			Dim p2 As New Point(X(i+1), Y(i+1))
			lines(i) = New Line(p1, p2)
			If lines(i).dx = 0 AndAlso lines(i).dy = 0 Then Exit Function
		Next i
		lines(N - 1) = New Line(New Point(X(N-1),Y(N-1)), New Point(X(0),Y(0)))
		lines(N) = lines(0)
		For i As Integer = 0 To N - 1
			If lines(i).IsPara(lines(i+1)) Then Exit Function
		Next i
		For i As Integer = 0 To N
			For j As Integer = 0 To N
				If Math.Abs(j - i) <= 1 Then Continue For
				If Math.Abs(j - i) >= N - 1 Then Continue For
				If lines(i).IsIntersect(lines(j)) Then
					 Console.WriteLine("intersect {0} {1}", i, j)
					 Console.WriteLine("({0}, {1}) - ({2}, {3})", lines(i).p1.x, lines(i).p1.y, lines(i).p2.x, lines(i).p2.y)
					 Console.WriteLine("({0}, {1}) - ({2}, {3})", lines(j).p1.x, lines(j).p1.y, lines(j).p2.x, lines(j).p2.y)
					 Exit Function
				End If
			Next j
		Next i
		Dim ret As BigInteger = 0
		For i As Integer = 0 To N - 1
			Dim ln As Line = lines(i)
			ret += ln.p1.x * ln.p2.y - ln.p1.y * ln.p2.x
		Next i
		If ret < 0 Then ret = -ret
		check = String.Format("{0:F01}", CDbl(ret) / 2.0)
	End Function
End Class

Visual Basic.Net Compiler version 0.0.0.5943 (Mono 4.0.1 - tarball)
Copyright (C) 2004-2010 Rolf Bjarne Kvinge. All rights reserved.

/home/sz6qsb/prog.vb (8,38) : error VBNC99999: vbnc crashed nearby this location in the source code.
vbnc : Command line : error VBNC99999: Unexpected error: Object reference not set to an instance of an object
  at vbnc.Parser.ParseList[T] (vbnc.BaseList`1[T] List, vbnc.Parser+ParseDelegate_Parent`1[T] ParseMethod, vbnc.ParsedObject Parent) [0x0003f] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseConstructedTypeName (vbnc.ParsedObject Parent) [0x0009b] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsNamespaceClause (vbnc.ParsedObject Parent) [0x000c7] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsAliasClause (vbnc.ParsedObject Parent) [0x00058] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsClause (vbnc.ParsedObject Parent) [0x0001e] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseList[T] (vbnc.BaseList`1[T] List, vbnc.Parser+ParseDelegate_Parent`1[T] ParseMethod, vbnc.ParsedObject Parent) [0x00005] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsClauses (vbnc.ImportsStatement Parent) [0x0000c] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsStatement (vbnc.ParsedObject Parent) [0x0001b] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseImportsStatements (vbnc.ParsedObject Parent) [0x0001e] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseFileHeader (vbnc.CodeFile CodeFile, vbnc.AssemblyDeclaration Assembly) [0x003b0] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.ParseAssemblyDeclaration (System.String RootNamespace, vbnc.AssemblyDeclaration assembly) [0x00089] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Parser.Parse (System.String RootNamespace, vbnc.AssemblyDeclaration assembly) [0x00007] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
  at vbnc.Compiler.Compile_Parse () [0x0008b] in <d77f4191aaaa4ed9a9a36d67dd32844d>:0 
Compilation took 00:00:00.6970110

Standard output is empty