VB.NET 随机唯一生成器

Question

我正在尝试使用下面的代码的 sn-p 生成一个唯一的随机数生成器，但它不起作用。 IF部分假设测试它是否是第一个生成的随机数，如果是，则假设将第一个随机数添加到ArrayList，如果它不是第一个随机数，则应该检查随机数是否已经在ArrayList，如果它在 ArrayList 中，它假设 MsgBox 并生成一个新的唯一随机数，该随机数不在 ArrayList 中并将其添加到 ArrayList，但它没有做任何这些。任何帮助将不胜感激。

Public Class Form1
    Dim r As New Random
    Dim dLowestVal As Integer = 1
    Dim dHighestVal As Integer = 26
    Dim dItemAmount As Integer = 1
    Dim RollCheck As New HashSet(Of Integer)

    Private Sub btnExit_Click(sender As Object, e As EventArgs) Handles btnExit.Click
        End
    End Sub

    Private Sub btnRollDice_Click(sender As Object, e As EventArgs) Handles btnRollDice.Click
        lblRandomNo.Text = r.Next(dLowestVal, dHighestVal)

        lblItemAmount.Text = dItemAmount

        If dItemAmount = 1 Then
            RollCheck.Add(Val(lblRandomNo.Text))
        ElseIf (RollCheck.Contains(Val(lblRandomNo.Text))) Then
            MsgBox("Already Exists")
            lblRandomNo.Text = r.Next(dLowestVal, dHighestVal)
            RollCheck.Add(Val(lblRandomNo.Text))
        End If

        dItemAmount = dItemAmount + 1

提前致谢。

Answer 1

您可以用这个简单的方法替换整个方法

' This is globally declared at the top of your form
Dim values As New List(Of Integer)

' This is called when you construct your form
' It will store consecutive integers from 1 to 25 (25 elements)
values = Enumerable.Range(1, 25).ToList()

这是从您的值中提取尚未使用的整数的方法

Private Sub Roll()
    ' Get an index in the values list
    Dim v = r.Next(0, values.Count)

    ' insert the value at that index to your RollCheck HashSet
    RollCheck.Add(values(v))

    ' Remove the found value from the values list, so the next call 
    ' cannot retrieve it again. 
    values.Remove(values(v))
End Sub

而且你可以通过这种方式从之前的事件处理程序中调用它

Private Sub btnRollDice_Click(sender As Object, e As EventArgs) Handles btnRollDice.Click
  if values.Count = 0 Then
      MessageBox("No more roll available")
  else
      Roll()
  End Sub
End Sub

Answer 2

HashSet 的要点在于，由于它不允许重复，因此您只需检查Add() 的返回值即可确定该数字是否已成功插入或是否已存在于列表中。

如果你想继续尝试直到成功，你所要做的就是将它包装在一个循环中：

If dHighestVal - dLowestVal >= RollCheck.Count Then
    'If the above check passes all unique values are MOST LIKELY already in the list. Exit to avoid infinite loop.
    MessageBox.Show("List is full!")
    Return 'Do not continue.
End If

Dim Num As Integer = r.Next(dLowestVal, dHighestVal)

'Iterate until a unique number was generated.
While Not RollCheck.Add(Num)
    MessageBox.Show("Already exists!")
    Num = r.Next(dLowestVal, dHighestVal)
End While

lblRandomNo.Text = Num

另一种编写循环的方法是：While RollCheck.Add(Num) = False。