你如何随机迭代一个没有重复的二维数组？

Question

您通常会使用两个 for 循环遍历二维数组：

For i = 0 to 5
   For j = 0 to 5
      Console.Writeline(Arr(i,j))
   Next
Next

我需要遍历一个 2D 数组（带有方形边 - 两边的长度相同，即 5x5 7x7 等），但我需要完全随机进行，并且不能重复相同的元素。

For Each i In iRandArr
   For Each j In jRandArr
      Console.Writeline(arr(iRandArr(j), jRandArr(i)))
   Next
Next
'note: the elements i and j are swapped round above in order to maintain the "column", "row" nomenclature

我已经尝试通过将每一边的长度推到一个列表中，将其随机化（即取消排序，参见here），然后以相同的双循环方式迭代。不幸的是，这种方法不是随机迭代，而是通过选择随机“列”并随机迭代“行”来进行半随机迭代。唯一的问题是迭代受列元素的限制，因此不是真正随机的（在编程意义上）。

有没有人可以尝试任何其他可能的选择？

Answer 1

很简单：

Dim Arr As Integer(,) =
    {{ 11, 12, 13 }, { 21, 22, 23 }, { 31, 32, 33 }}

Dim random As New Random

Dim indices = _
        Enumerable _
            .Range(0, 3) _
            .SelectMany(Function(i) _
                Enumerable _
                    .Range(0, 3) _
                    .Select(Function(j) (i, j))) _
            .OrderBy(Function(x) random.Next())
            
For Each x In indices
    Console.Writeline(Arr(x.i, x.j))
Next

这只是生成所有可能的索引对，然后随机打乱它们。这样可以确保没有重复。

在这个例子中我得到：

23
32
22
13
33
12
11
31
21

Answer 2

这是我评论中该想法的完整编译实现：

1. 构建一维point对象集，代表二维数组中的位置
2. 随机化一维点集
3. 迭代随机集

请注意，使用自定义 Point 结构的选择是可选的；你可以使用任何你想要的类/结构类型，甚至是Tuple。随机化算法也是如此 - 使用你想要的任何东西。下面的代码只是问题中链接中相同逻辑的一个奇特的 LINQ 实现。

Option Explicit On
Option Strict On
Option Infer Off
Option Compare Binary

Imports System
Imports System.Collections.Generic
Imports System.Linq

Module Module1

    Sub Main()
        'init an array
        ' this is just for testing purposes;
        ' presumably the 'real' array comes from somewhere else
        Console.WriteLine("Original Array Ordering:")
        Const arrayMaxIndex As Integer = 5
        Dim arr(arrayMaxIndex, arrayMaxIndex) As Integer
        Dim value As Integer = 0
        For row As Integer = 0 To arrayMaxIndex
            For col As Integer = 0 To arrayMaxIndex
                Console.WriteLine($"Row: {row} | Col: {col} | Value: {value}")
                arr(row, col) = value
                value += 1
            Next
        Next

        'build a 1D list of points that refer to array locations
        ' this is written separately from initializing the 2D array on purpose,
        ' since the assumption is that it will be used on an array of unknown origin
        Dim pointList As New List(Of Point)
        For row As Integer = 0 To arr.GetUpperBound(0)
            For col As Integer = 0 To arr.GetUpperBound(1)
                pointList.Add(New Point(row, col))
            Next
        Next

        'randomize the 1D list
        ' choose whatever randomization algorithm you want; this is just one implementation
        Dim rnd As New Random
        Dim randomizedList As IEnumerable(Of Point) = pointList.OrderBy(Function() rnd.Next())

        'step through the randomized 1D list
        Console.WriteLine()
        Console.WriteLine("Randomized Array Ordering:")
        For Each p As Point In randomizedList
            Console.WriteLine($"Row: {p.Row} | Col: {p.Col} | Value: {arr(p.Row, p.Col)}")
        Next

    End Sub

End Module

'use whatever Point type you want
' Didn't want to hard-code to System.Drawing
Friend Structure Point
    Public Sub New(row As Integer, col As Integer)
        _Row = row
        _Col = col
    End Sub

    Public ReadOnly Property Row As Integer
    Public ReadOnly Property Col As Integer
End Structure

示例输出（说明没有重复的“随机性”）：

Original Array Ordering:
Row: 0 | Col: 0 | Value: 0
Row: 0 | Col: 1 | Value: 1
Row: 0 | Col: 2 | Value: 2
Row: 0 | Col: 3 | Value: 3
Row: 0 | Col: 4 | Value: 4
Row: 0 | Col: 5 | Value: 5
Row: 1 | Col: 0 | Value: 6
Row: 1 | Col: 1 | Value: 7
Row: 1 | Col: 2 | Value: 8
Row: 1 | Col: 3 | Value: 9
Row: 1 | Col: 4 | Value: 10
Row: 1 | Col: 5 | Value: 11
Row: 2 | Col: 0 | Value: 12
Row: 2 | Col: 1 | Value: 13
Row: 2 | Col: 2 | Value: 14
Row: 2 | Col: 3 | Value: 15
Row: 2 | Col: 4 | Value: 16
Row: 2 | Col: 5 | Value: 17
Row: 3 | Col: 0 | Value: 18
Row: 3 | Col: 1 | Value: 19
Row: 3 | Col: 2 | Value: 20
Row: 3 | Col: 3 | Value: 21
Row: 3 | Col: 4 | Value: 22
Row: 3 | Col: 5 | Value: 23
Row: 4 | Col: 0 | Value: 24
Row: 4 | Col: 1 | Value: 25
Row: 4 | Col: 2 | Value: 26
Row: 4 | Col: 3 | Value: 27
Row: 4 | Col: 4 | Value: 28
Row: 4 | Col: 5 | Value: 29
Row: 5 | Col: 0 | Value: 30
Row: 5 | Col: 1 | Value: 31
Row: 5 | Col: 2 | Value: 32
Row: 5 | Col: 3 | Value: 33
Row: 5 | Col: 4 | Value: 34
Row: 5 | Col: 5 | Value: 35

Randomized Array Ordering:
Row: 2 | Col: 5 | Value: 17
Row: 3 | Col: 2 | Value: 20
Row: 1 | Col: 0 | Value: 6
Row: 2 | Col: 1 | Value: 13
Row: 4 | Col: 0 | Value: 24
Row: 3 | Col: 5 | Value: 23
Row: 4 | Col: 2 | Value: 26
Row: 5 | Col: 1 | Value: 31
Row: 1 | Col: 5 | Value: 11
Row: 0 | Col: 2 | Value: 2
Row: 4 | Col: 5 | Value: 29
Row: 0 | Col: 5 | Value: 5
Row: 4 | Col: 1 | Value: 25
Row: 3 | Col: 0 | Value: 18
Row: 0 | Col: 4 | Value: 4
Row: 0 | Col: 0 | Value: 0
Row: 1 | Col: 4 | Value: 10
Row: 4 | Col: 3 | Value: 27
Row: 5 | Col: 0 | Value: 30
Row: 2 | Col: 2 | Value: 14
Row: 1 | Col: 1 | Value: 7
Row: 3 | Col: 1 | Value: 19
Row: 2 | Col: 0 | Value: 12
Row: 2 | Col: 4 | Value: 16
Row: 5 | Col: 2 | Value: 32
Row: 0 | Col: 1 | Value: 1
Row: 4 | Col: 4 | Value: 28
Row: 5 | Col: 5 | Value: 35
Row: 1 | Col: 2 | Value: 8
Row: 5 | Col: 4 | Value: 34
Row: 5 | Col: 3 | Value: 33
Row: 1 | Col: 3 | Value: 9
Row: 2 | Col: 3 | Value: 15
Row: 0 | Col: 3 | Value: 3
Row: 3 | Col: 3 | Value: 21
Row: 3 | Col: 4 | Value: 22

附：我希望你不要关心这里的性能；这确实是一个蛮力实现。