How to shift the start of an array in C#?

Question

I\'m trying to reorganize an array based on the first occurrence of a value (thus simulating similar functionality to a circular array.)

For example, in the followin

Answer 1

To begin with, do a linear search to find the first occurrence of the value that you want to make the first element:

// value contains the value to find.

int skip;
for (int i = 0; i < array.Length; i++)
{
    if (array[i] == value)
    {
        skip = i;
        break;
    }
}

// skip contains the index of the element to put at the front.
// Equivalently, it is the number of items to skip.
// (I chose this name for it because it makes the subtractions
// in the Array.Copy implementation more intuitive.)

Do you want to change the actual array? Then do what Thorsten Dittmar suggests:

int[] array = new int[] { 2, 3, 6, 1, 7, 6 };
int[] result = new int[array.Length];

int skip = 2; // So that array[skip] will be result[0] at the end

Array.Copy(array, skip, result, 0, array.Length - skip);
Array.Copy(array, 0, result, array.Length - skip, skip);

Do you want to just view the array in the new order, without doing anything else? Then index it like so:

array[(i + skip) % array.Length]  // Instead of array[i]

Edit: Just for laughs, an implementation of Jon Skeet's suggestion to implement the copy while using only a single buffer value (sourceValue):

// GCD gives the greatest common divisor
int gcd = GCD(array.Length, skip);

// period is the length of the permutation cycles in our rotation.
int period = array.Length / gcd;

int max = array.Length / period;
for (int i = 0; i < max; i++)
{
    int sourceIndex = i;
    int sourceValue = array[sourceIndex];

    for (int n = 1; n <= period; n++)
    {
        int destinationIndex = (sourceIndex + array.Length - skip) % array.Length;

        int temp = array[destinationIndex];
        array[destinationIndex] = sourceValue;
        sourceValue = temp;

        sourceIndex = destinationIndex;
    }
}