How to change position of an element in an array? - arrays

Question

If I have an array, for example this
Dim Players() As String = {"Adam", "Helen", "Jack", "Emily"}
How do I change the position of each element by a value, for example if by 1, Adam will move to 2, Helen will move to 3, and Emily should come back to 1.
I was able to do this if increment by 1. I would have the last element stored in a variable and when done moving all elements by 1, I would set the first element to the variable(Emily in this case).
How would I do it if having different increment values like 2, 3, 4, or even 6?
Edit: Any programming language is fine but it has to be done with for loops and no functions.
Update: I am an IGCSE student and this question is bugging from over a week.

Answer 1

If you can do an increment of one, just repeat that the required number of times.
A better way would be: (let's call the increment n); store the end n elements in another array; move the elements before that towards the end of the array; copy back the elements from the other array to the start. Like this:
Module Module1
Sub Main()
Dim players() As String = {"Adam", "Becky", "Clive", "Debby", "Edward", "Fiona"}
Dim rotateBy = 2
' make sure shiftBy is in a usable range
rotateBy = rotateBy Mod players.Length
' if shiftBy is negative, make it positive such that a left-rotate is performed
If rotateBy < 0 Then
rotateBy = rotateBy + players.Length
End If
' store the elements which will be moved to the other end of the array
Dim tmp(rotateBy - 1) As String
Dim startIndex = players.Length - rotateBy
For i = startIndex To players.Length - 1
tmp(i - startIndex) = players(i)
Next
' move the elements
For i = players.Length - 1 - rotateBy To 0 Step -1
players(i + rotateBy) = players(i)
Next
'fill in the other elements
For i = 0 To rotateBy - 1
players(i) = tmp(i)
Next
' show the result
Console.WriteLine(String.Join(", ", players))
Console.ReadLine()
End Sub
End Module
Note that the copying of elements within the players array is done backwards so that an overlapping range does not splat over values which have yet to be moved.
To shift the elements backwards, use a negative value for rotateBy.
If you are using a language with a function which gives array copying functions, this method is easy to adapt to use that functionality. For anyone wondering about that in the future:
Module Module1
Sub Main()
Dim players() As String = {"Adam", "Becky", "Clive", "Debby", "Edward", "Fiona"}
Dim rotateBy = 4
' make sure shiftBy is in a usable range
rotateBy = rotateBy Mod players.Length
' if shiftBy is negative, make it positive such that a left-rotate is performed
If rotateBy < 0 Then
rotateBy = rotateBy + players.Length
End If
' store the elements which will be moved to the other end of the array
Dim tmp(rotateBy - 1) As String
Dim startIndex = players.Length - rotateBy
Array.Copy(players, startIndex, tmp, 0, rotateBy)
Array.Copy(players, 0, players, rotateBy, startIndex)
Array.Copy(tmp, players, tmp.Length)
' show the result
Console.WriteLine(String.Join(", ", players))
Console.ReadLine()
End Sub
End Module
As you mentioned any programming language, this is what it could be in C# as a function but without using any framework methods such as Array.Copy:
public static void RotateUsingLoops<T>(T[] elements, int rotateBy)
{
rotateBy = rotateBy % elements.Length;
if (rotateBy < 0)
{
rotateBy += elements.Length;
}
T[] tmp = new T[rotateBy];
int startIndex = elements.Length - rotateBy;
// store the elements which will be moved to the other end of the array
for (int i = startIndex; i < elements.Length; i++)
{
tmp[i - startIndex] = elements[i];
}
// move the elements
for (int i = elements.Length - 1 - rotateBy; i >= 0; i--)
{
elements[i + rotateBy] = elements[i];
}
// fill in the other elements
for (int i = 0; i < rotateBy; i++)
{
elements[i] = tmp[i];
}
}
Whereby you could use
static void Main(string[] args)
{
var a = new string[] { "A", "B", "C", "D" };
RotateUsingLoops(a, 2);
Console.WriteLine(string.Join(", ", a));
Console.ReadLine();
}
to get an output of:
C, D, A, B

Answer 2

Circular array rotation is what you are referring towards.
In VB.NET the following code will rotate an array of elements to the Right, by the Shift amount.
Sub Main()
Dim Players() As String = {"Adam", "Helen", "Jack", "Emily"}
Dim Players_Shifted(Players.Length - 1) As String
Dim Shift As Integer = 2
If Shift > Players.Length Then
Shift = Shift Mod Players.Length
End If
For index = 0 To Shift - 1
Players_Shifted(index) = Players(Players.Length - Shift + index)
Next
Dim index_2 = 0
For index = Shift To Players.Length - 1
Players_Shifted(index) = Players(index_2)
index_2 = index_2 + 1
Next
Players = Players_Shifted
' Print out Players Array '
For index = 0 To Players.Length - 1
Console.Write(Players(index) + ", ")
Next
Console.ReadLine()
End Sub

Answer 3

Here is a snippet of a C++ code that implements this functionality-
Let temp be a temporary variable, N be the size of the array, shift be the number of places u wanna shift and arr be the original array.
int temp = arr[0];
int i = 0;
while(True){
//swap(arr(i + shift)%N, temp);
swap_var = temp;
temp = arr[(i+shift)%N];
arr[(i+shift)%N] = swap_var;
i = (i+shift)%N;
if (i == 0){
break;
}
}
Edit: Using for loop.
int temp = arr[0]; //change int to the type of variable ur array is
int i =0;
for (int count = 0; count<N ; count++){
//swap(arr(i + shift)%N, temp);
swap_var = temp;
temp = arr[(i+shift)%N];
arr[(i+shift)%N] = swap_var;
i = (i+shift)%N;
}