using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list1 = new [] {1,2,3};

        var list2 = new [] {1,3,0};

        var h1 = GetOrderIndependentHashCode2(list1);

        var h2 = GetOrderIndependentHashCode2(list2);

        Console.WriteLine(h1);

        Console.WriteLine(h2);

    }

    public static int GetOrderIndependentHashCode<T>(IEnumerable<T> source)

    {

        int hash = 17;

        foreach (T element in source)

        {

            int h = EqualityComparer<T>.Default.GetHashCode(element);

            if (h != 0)

                hash = unchecked (hash * h);

        }

        return hash;

    }

    public static int GetOrderIndependentHashCode2<T>(IEnumerable<T> source)

    {

        int hash = 0;

        int curHash;

        int bitOffset = 0;

        // Stores number of occurences so far of each value.

        var valueCounts = new Dictionary<T, int>();

​

        foreach (T element in source)

        {

            curHash = EqualityComparer<T>.Default.GetHashCode(element);

            if (valueCounts.TryGetValue(element, out bitOffset))

                valueCounts[element] = bitOffset + 1;

            else

                valueCounts.Add(element, bitOffset);

​

            // The current hash code is shifted (with wrapping) one bit

            // further left on each successive recurrence of a certain

            // value to widen the distribution.

            // 37 is an arbitrary low prime number that helps the

            // algorithm to smooth out the distribution.

            hash = unchecked(hash + ((curHash << bitOffset) |

                (curHash >> (32 - bitOffset))) * 37);

        }

​

        return hash;

    }

}