Public Class Form1
    Private Const N = 200, M = 200
    Private Const N1 = N - 1, M1 = M - 1
    Private A(N1, M1) As Byte : Private D(N, M) As Byte
    Private HX(N * M), HY(N * M)
    Dim img As New Bitmap(200, 200) '300x300サイズのImage
    Private Sub セル初期設定()
        For i = 0 To N1
            For j = 0 To M1
                A(i, j) = 0 : D(i, j) = 0
            Next
        Next
    End Sub
    Private Sub セル設定() ' 乱数によるセル設定
        Dim X As Integer, Y As Integer
        Do : X = Int(N * Rnd()) : Y = Int(M * Rnd())
        Loop Until A(Y, X) = 0
        A(Y, X) = 1 : img.SetPixel(X, Y, Color.Black)
    End Sub
    
    Private Function 浸透() As Long
        セル初期設定() : Randomize()
        For i = 1 To M1
            セル設定()
        Next
        For i = M1 To 40000
            If (i Mod 200) = 0 Then
                Label1.Text = i : Me.Refresh()
            End If
            セル設定()
            If 判定() Then
                浸透 = i : Exit Function
            End If
        Next
        浸透 = -1
    End Function
    Private Function 方向判定(i As Integer, j As Integer, K As Integer) As Boolean
        If j > M1 Then
            方向判定 = True
            For ii = 0 To K - 1
                img.SetPixel(HX(ii), HY(ii), Color.Red)
            Next
        ElseIf j < 0 Or i < 0 Or i > M1 Then : 方向判定 = False
        ElseIf D(i, j) <> 0 Then : 方向判定 = False
        Else
            D(i, j) = 1  '　以前来たことがあることを示すフラグ
            If A(i, j) = 0 Then
                方向判定 = False
            Else
                HX(K) = j : HY(K) = i
                方向判定 = 方向判定(i, j + 1, K + 1) '　ｊ正方向試行
                If 方向判定 Then Exit Function
                方向判定 = 方向判定(i, j - 1, K + 1) '　ｊ負方向試行
                If 方向判定 Then Exit Function
                方向判定 = 方向判定(i + 1, j, K + 1) '　i正方向試行
                If 方向判定 Then Exit Function
                方向判定 = 方向判定(i - 1, j, K + 1) '　i負方向試行
            End If
        End If
    End Function
    Private Function 判定() As Boolean
        Dim S As Byte
        For i = 0 To N1
            For j = 0 To M1
                D(i, j) = 0
            Next
        Next
        判定 = True
        For i = 0 To N1
            If A(i, 0) <> 0 Then
                S = 方向判定(i, 0, 0) : If S Then Exit Function
            End If
        Next
        判定 = False
    End Function
    Private Function coff() As Double
        Dim CC As Integer
        For i = 0 To N1
            For j = 0 To M1
                If A(i, j) <> 0 Then CC = CC + 1
            Next
        Next
        coff = 100.0 * CC / CDbl(N * M)
    End Function
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Dim j As Integer
        Dim g As Graphics = Graphics.FromImage(img) : g.Clear(Color.White) '描画クリア
        Cursor.Current = Cursors.WaitCursor '描画処理中、カーソルを待ち状態にする
        j = 浸透() : Label1.Text = ""
        PictureBox1.Image = img : g.Dispose() 'リソースを解放する
        If j < 0 Then
            MsgBox("試行に失敗しました")
        Else
            MsgBox("試行回数 = " & j & "  比率　" & Format(coff(), "##0.00") & " %")
        End If
        Cursor.Current = Cursors.Default '
    End Sub
End Class