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I am trying to write a function which iterates through an array and when it finds a certain type of value it will shift it to the right a defined number of places.

I know how to shift elements by temporarily storing a value, shifting the right side elements to the left and then writing the temporary value in the correct place.

The bit I am struggling with is if the certain character appears near the end of the array I need it to wrap around and continue from the start of the array, so is circular.

So an array shifting, for example, capital letters to the right 3 places and special characters to the left 1 place:

{ M, y, N, a, m, e, P} becomes...
{ y, M, P, a, N, m, e}

To shift an element of 8 to the right 3 places I have below, but this only works if 8 appears earlier than 3 elements from the end of the array and will not wrap around.

input array:

{0, 1, 2, 3, 4, 5, 6, 7, **8**, 9}

desired output:

{0, **8**, 1, 2, 3, 4, 5, 6, 7, 9}

int[] array = new int[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

for (int i = array.Length - 1; i >= 0; i--) 
{
    if (array[i] == 8) 
    {
        int temp = array[i];
        int j = 0;
        for (j = i; j < i + 3; j++) 
        {
            array[j] = array[j + 1];
        }
        array[j] = temp;
    }
}
double-beep
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MarkJW
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  • What exactly are you having problems with? – Oded Apr 17 '11 at 19:03
  • its the continuation to the start of the array which I need help on, so if the element needed to be shifted to the right appears as the second to last element and needs to be shifted three to the right it will end up as the second element in the array – MarkJW Apr 17 '11 at 19:07

2 Answers2

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Just use modulo arithmetic so that instead of writing to the element at index j as you shift, instead write to the element at index j % array.Length. Thusly:

public void FindAndShift<T>(T[] array, T value, int shift) {
    int index = Array.IndexOf(array, value);
    int shiftsRemaining = shift;
    for(int currentPosition = index; shiftsRemaining > 0; shiftsRemaining--) {
        array[currentPosition % array.Length] = array[(currentPosition + 1) % array.Length];
    }
    array[(index + shift) % array.Length] = value;
}

I have excluded error checking.

jason
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You can do it with an if statement, check if there is room enough before the end of the array and if it isn't you have to calculate how many steps to shift in the beginning of the array aswell.

I also think that you can do it by calculating the positions modulo the length of the array when you do the shifting, I can't try it at the moment but the logic in my head says that it should work.

mylopeda
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  • If the logic in your head is like the one Jason has said then it does indeed work :) Thank you – MarkJW Apr 17 '11 at 19:29