Cycle Sort

Pseudocode Implementation

(input)
output = 0
for cycleStart from 0 to length(array) - 2
    item = array[cycleStart]
    pos = cycleStart
    for i from cycleStart + 1 to length(array) - 1
        if array[i] < item:
            pos += 1
    if pos == cycleStart:
        continue
    while item == array[pos]:
        pos += 1
    array[pos], item = item, array[pos]
    writes += 1
    while pos != cycleStart:
        pos = cycleStart
        for i from cycleStart + 1 to length(array) - 1
            if array[i] < item:
                pos += 1
        while item == array[pos]:
            pos += 1
        array[pos], item = item, array[pos]
        writes += 1
return outout

Cycle Sort Basic Information

Cycle Sort (opens new window) is sorting algorithm which uses comparison sort (opens new window) that is theoretically optimal in terms of the total number of writes to original array, unlike any other in-place sorting algorithm. Cycle sort is unstable sorting algorithm. It is based on idea of permutation in which permutations are factored into cycles, which individually rotate and return a sorted output.

Example of Cycle Sort:

(opens new window)

Auxiliary Space: O(1)
Time Complexity: O(n^2)

C# Implementation

public class CycleSort
{
    public static void SortCycle(int[] input)
    {
        for (var i = 0; i < input.Length; i++)
        {
            var item = input[i];
            var position = i;
            do
            {
                var k = input.Where((t, j) => position != j && t < item).Count();
                if (position == k) continue;
                while (position != k && item == input[k])
                {
                    k++;
                }
                var temp = input[k];
                input[k] = item;
                item = temp;
                position = k;
            } while (position != i);
        }
    }

    public static int[] Main(int[] input)
    {
        SortCycle(input);
        return input;
    }
}