C# Permutation of an array of arraylists?

Question

I have an ArrayList[] myList and I am trying to create a list of all the permutations of the values in the arrays.

EXAMPLE: (all values are strings)

Answer 1

I'm surprised nobody posted the LINQ solution.

from val0 in new []{ "1", "5", "3", "9" }
from val1 in new []{ "2", "3" }
from val2 in new []{ "93" }
select String.Format("val0={0};val1={1};val2={2}", val0, val1, val2)

Answer 2

Recursive solution

    static List<string> foo(int a, List<Array> x)
    {
        List<string> retval= new List<string>();
        if (a == x.Count)
        {
            retval.Add("");
            return retval;
        }
        foreach (Object y in x[a])
        {
            foreach (string x2 in foo(a + 1, x))
            {
                retval.Add(y.ToString() + " " + x2.ToString());
            }

        }
        return retval;
    }
    static void Main(string[] args)
    {
        List<Array> myList = new List<Array>();
        myList.Add(new string[0]);
        myList.Add(new string[0]);
        myList.Add(new string[0]);
        myList[0] = new string[]{ "1", "5", "3", "9" };
        myList[1] = new string[] { "2", "3" };
        myList[2] = new string[] { "93" };
        foreach (string x in foo(0, myList))
        {
            Console.WriteLine(x);
        }

        Console.ReadKey();
    }

Note that it would be pretty easy to return a list or array instead of a string by changing the return to be a list of lists of strings and changing the retval.add call to work with a list instead of using concatenation.

How it works:

This is a classic recursive algorithm. The base case is foo(myList.Count, myList), which returns a List containing one element, the empty string. The permutation of a list of n string arrays s1, s2, ..., sN is equal to every member of sA1 prefixed to the permutation of n-1 string arrays, s2, ..., sN. The base case is just there to provide something for each element of sN to be concatenated to.

Answer 3

I recently ran across a similar problem in a project of mine and stumbled on this question. I needed a non-recursive solution that could work with lists of arbitrary objects. Here's what I came up with. Basically I'm forming a list of enumerators for each of the sub-lists and incrementing them iteratively.

public static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<IEnumerable<T>> lists)
{
    // Check against an empty list.
    if (!lists.Any())
    {
        yield break;
    }

    // Create a list of iterators into each of the sub-lists.
    List<IEnumerator<T>> iterators = new List<IEnumerator<T>>();
    foreach (var list in lists)
    {
        var it = list.GetEnumerator();
        // Ensure empty sub-lists are excluded.
        if (!it.MoveNext())
        {
            continue;
        }
        iterators.Add(it);
    }

    bool done = false;
    while (!done)
    {
        // Return the current state of all the iterator, this permutation.
        yield return from it in iterators select it.Current;

        // Move to the next permutation.
        bool recurse = false;
        var mainIt = iterators.GetEnumerator();
        mainIt.MoveNext(); // Move to the first, succeeds; the main list is not empty.
        do
        {
            recurse = false;
            var subIt = mainIt.Current;
            if (!subIt.MoveNext())
            {
                subIt.Reset(); // Note the sub-list must be a reset-able IEnumerable!
                subIt.MoveNext(); // Move to the first, succeeds; each sub-list is not empty.

                if (!mainIt.MoveNext())
                {
                    done = true;
                }
                else
                {
                    recurse = true;
                }
            }
        }
        while (recurse);
    }
}

Answer 4

One of the problems I encountred when I was doing this for a very large amount of codes was that with the example brian was given I actually run out of memory. To solve this I used following code.

static void foo(string s, List<Array> x, int a)
    {
        if (a == x.Count)
        {
            // output here
            Console.WriteLine(s);
        }
        else
        {
            foreach (object y in x[a])
            {
                foo(s + y.ToString(), x, a + 1);
            }
        }
    }

static void Main(string[] args)
    {
        List<Array> a = new List<Array>();
        a.Add(new string[0]);
        a.Add(new string[0]);
        a.Add(new string[0]);
        a[0] = new string[] { "T", "Z" };
        a[1] = new string[] { "N", "Z" };
        a[2] = new string[] { "3", "2", "Z" };

        foo("", a, 0);
        Console.Read();
    }

Answer 5

private static void GetP(List<List<string>> conditions, List<List<string>> combinations, List<string> conditionCombo, List<string> previousT, int selectCnt)
{
    for (int i = 0; i < conditions.Count(); i++)
    {
        List<string> oneField = conditions[i];
        for (int k = 0; k < oneField.Count(); k++)
        {
            List<string> t = new List<string>(conditionCombo);
            t.AddRange(previousT);
            t.Add(oneField[k]);

            if (selectCnt == t.Count )
            {
                combinations.Add(t);
                continue;
            }
            GetP(conditions.GetRange(i + 1, conditions.Count - 1 - i), combinations, conditionCombo, t, selectCnt);
        }

    }
}

List<List<string>> a = new List<List<string>>();
a.Add(new List<string> { "1", "5", "3", "9" });
a.Add(new List<string> { "2", "3" });
a.Add(new List<string> { "93" });
List<List<string>> result = new List<List<string>>();
GetP(a, result, new List<string>(), new List<string>(), a.Count);

Another recursive function.

Answer 6

This will work no matter how many arrays you add to your myList:

        static void Main(string[] args)
        {
            string[][] myList = new string[3][];
            myList[0] = new string[] { "1", "5", "3", "9" };
            myList[1] = new string[] { "2", "3" };
            myList[2] = new string[] { "93" };

            List<string> permutations = new List<string>(myList[0]);

            for (int i = 1; i < myList.Length; ++i)
            {
                permutations = RecursiveAppend(permutations, myList[i]);
            }

            //at this point the permutations variable contains all permutations

        }

        static List<string> RecursiveAppend(List<string> priorPermutations, string[] additions)
        {
            List<string> newPermutationsResult = new List<string>();
            foreach (string priorPermutation in priorPermutations)
            {
                foreach (string addition in additions)
                {
                    newPermutationsResult.Add(priorPermutation + ":" + addition);
                }
            }
            return newPermutationsResult;
        }

Note that it's not really recursive. Probably a misleading function name.

Here is a version that adheres to your new requirements. Note the section where I output to console, this is where you can do your own formatting:

static void Main(string[] args)
        {
            string[][] myList = new string[3][];
            myList[0] = new string[] { "1", "5", "3", "9" };
            myList[1] = new string[] { "2", "3" };
            myList[2] = new string[] { "93" };

            List<List<string>> permutations = new List<List<string>>();

            foreach (string init in myList[0])
            {
                List<string> temp = new List<string>();
                temp.Add(init);
                permutations.Add(temp);
            }

            for (int i = 1; i < myList.Length; ++i)
            {
                permutations = RecursiveAppend(permutations, myList[i]);
            }

            //at this point the permutations variable contains all permutations

            foreach (List<string> list in permutations)
            {
                foreach (string item in list)
                {
                    Console.Write(item + ":");
                }
                Console.WriteLine();
            }

        }

        static List<List<string>> RecursiveAppend(List<List<string>> priorPermutations, string[] additions)
        {
            List<List<string>> newPermutationsResult = new List<List<string>>();
            foreach (List<string> priorPermutation in priorPermutations)
            {
                foreach (string addition in additions)
                {
                    List<string> priorWithAddition = new List<string>(priorPermutation);
                    priorWithAddition.Add(addition);
                    newPermutationsResult.Add(priorWithAddition);
                }
            }
            return newPermutationsResult;
        }