Task: Card shuffles
C: #include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

void init() {
    srand((unsigned int)time(NULL));
}

int random(int low, int high) {
    int diff, val;

    diff = high - low;
    if (diff == 0) {
        return low;
    }

    val = rand() % diff;
    return val + low;
}

void initDeck(int *deck, const int size) {
    int i;
    for (i = 0; i < size; ++i) {
        *deck++ = i + 1;
    }
}

void writeDeck(const int *deck, const int size) {
    int i;

    printf("[");
    if (size > 0) {
        printf("%d", *deck++);
    }
    for (i = 1; i < size; ++i) {
        printf(", %d", *deck++);
    }
    printf("]");
}

void riffleShuffle(int * const deck, const int size, int flips) {
    int n, cutPoint, nlp, lp, rp, bound;
    int *nl;

    nl = (int *)malloc(size * sizeof(int));

    for (n = 0; n < flips; ++n) {
        cutPoint = size / 2;
        if (random(0, 2) > 0) {
            cutPoint = cutPoint + random(0, size / 10);
        } else {
            cutPoint = cutPoint - random(0, size / 10);
        }

        nlp = 0;
        lp = 0;
        rp = cutPoint;

        while (lp < cutPoint && rp < size) {
            
            bound = (cutPoint - lp) * 50 / (size - rp);
            if (random(0, 50) >= bound) {
                nl[nlp++] = deck[rp++];
            } else {
                nl[nlp++] = deck[lp++];
            }
        }
        while (lp < cutPoint) {
            nl[nlp++] = deck[lp++];
        }
        while (rp < size) {
            nl[nlp++] = deck[rp++];
        }

        memcpy(deck, nl, size * sizeof(int));
    }

    free(nl);
}

void overhandShuffle(int * const mainHand, const int size, int passes) {
    int n, cutSize, mp, op, tp, i;
    int *otherHand, *temp;

    otherHand = (int *)malloc(size * sizeof(int));
    temp = (int *)malloc(size * sizeof(int));

    for (n = 0; n < passes; ++n) {
        mp = 0;
        op = 0;
        tp = 0;

        while (mp < size) {
            cutSize = random(0, size / 5) + 1;

            
            for (i = 0; i < cutSize && mp < size; ++i) {
                temp[tp++] = mainHand[mp++];
            }

            
            if (random(0, 10) >= 1) {
                

                
                for (i = op - 1; i >= 0; --i) {
                    otherHand[i + tp] = otherHand[i];
                }

                
                memcpy(otherHand, temp, tp * sizeof(int));
                op += tp;
                tp = 0;
            } else {
                
                for (i = 0; i < tp; ++i, ++op) {
                    otherHand[op] = temp[i];
                }
                tp = 0;
            }
        }

        
        memcpy(mainHand, otherHand, size * sizeof(int));
    }

    free(otherHand);
    free(temp);
}

#define SIZE 20
int main() {
    int deck[SIZE];

    init();

    printf("Riffle shuffle\n");
    initDeck(deck, SIZE);
    writeDeck(deck, SIZE);
    printf("\n");
    riffleShuffle(deck, SIZE, 10);
    writeDeck(deck, SIZE);
    printf("\n\n");

    printf("Riffle shuffle\n");
    initDeck(deck, SIZE);
    writeDeck(deck, SIZE);
    printf("\n");
    riffleShuffle(deck, SIZE, 1);
    writeDeck(deck, SIZE);
    printf("\n\n");

    printf("Overhand shuffle\n");
    initDeck(deck, SIZE);
    writeDeck(deck, SIZE);
    printf("\n");
    overhandShuffle(deck, SIZE, 10);
    writeDeck(deck, SIZE);
    printf("\n\n");

    printf("Overhand shuffle\n");
    initDeck(deck, SIZE);
    writeDeck(deck, SIZE);
    printf("\n");
    overhandShuffle(deck, SIZE, 1);
    writeDeck(deck, SIZE);
    printf("\n\n");

    return 0;
}

VB: Imports System.Runtime.CompilerServices
Imports System.Text

Module Module1

    <Extension()>
    Function AsString(Of T)(c As ICollection(Of T)) As String
        Dim sb = New StringBuilder("[")
        sb.Append(String.Join(", ", c))
        Return sb.Append("]").ToString()
    End Function

    Private rand As New Random()

    Function RiffleShuffle(Of T)(list As ICollection(Of T), flips As Integer) As List(Of T)
        Dim newList As New List(Of T)(list)

        For n = 1 To flips
            
            Dim cutPoint As Integer = newList.Count / 2 + If(rand.Next(0, 2) = 0, -1, 1) * rand.Next(newList.Count * 0.1)

            
            Dim left As New List(Of T)(newList.Take(cutPoint))
            Dim right As New List(Of T)(newList.Skip(cutPoint))

            newList.Clear()

            While left.Count > 0 AndAlso right.Count > 0
                
                
                
                If rand.NextDouble() >= left.Count / right.Count / 2 Then
                    newList.Add(right.First())
                    right.RemoveAt(0)
                Else
                    newList.Add(left.First())
                    left.RemoveAt(0)
                End If
            End While

            
            If left.Count > 0 Then
                newList.AddRange(left)
            End If
            If right.Count > 0 Then
                newList.AddRange(right)
            End If
        Next

        Return newList
    End Function

    Function OverhandShuffle(Of T)(list As ICollection(Of T), passes As Integer) As List(Of T)
        Dim mainHand As New List(Of T)(list)

        For n = 1 To passes
            Dim otherhand = New List(Of T)

            While mainHand.Count > 0
                
                Dim cutSize = rand.Next(list.Count * 0.2) + 1

                Dim temp = New List(Of T)

                
                Dim i = 0
                While i < cutSize AndAlso mainHand.Count > 0
                    temp.Add(mainHand.First())
                    mainHand.RemoveAt(0)
                    i = i + 1
                End While

                
                If rand.NextDouble() >= 0.1 Then
                    
                    temp.AddRange(otherhand)
                    otherhand = temp
                Else
                    
                    otherhand.AddRange(temp)
                End If
            End While

            
            mainHand = otherhand
        Next

        Return mainHand
    End Function

    Sub Main()
        Dim list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = RiffleShuffle(list, 10)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = RiffleShuffle(list, 1)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = OverhandShuffle(list, 10)
        Console.WriteLine(list.AsString())
        Console.WriteLine()

        list = New List(Of Integer)(Enumerable.Range(1, 20))
        Console.WriteLine(list.AsString())
        list = OverhandShuffle(list, 1)
        Console.WriteLine(list.AsString())
        Console.WriteLine()
    End Sub

End Module