all possible combinations between certain amount of digits c#

Question

I need to find a function that works like this:

 int[] matches = getAllPossibleCombinations(
    int lengthOfEachIntReturnedInArray, 
    List<char> typesOfElementsUsedInCombinations);

input elements would be these (this is just an example):

int lengthofeachintreturnedinarray = (int) 2
List<char> typesofelementsusedincombinations = {a,b}

then the output would have to be (in a string array):

aa

ab

ba

bb

Each individual output element in the array must have a length defined by the first argument in the method (in this case 2) and must contain all possible combinations between the given letters in the second argument

I have seen something about powersets, should I use them, or should foreach loops suit the job?

! the proposed question with answer above is NOT the same, it doesn't use set lenghts !

do you want the second argument to be a List<string> or a List<char> ? i.e., can the individual elements be more than one character each ? — Charles Bretana

p.s.w.g p.s.w.g · Accepted Answer · 2013-09-05T16:32:39

I'll direct you to Eric Lippert's article on implementing a Cartesian Product in Linq, which he writes as an extension method.

static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences) 
{ 
  IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() }; 
  return sequences.Aggregate( 
    emptyProduct, 
    (accumulator, sequence) => 
      from accseq in accumulator 
      from item in sequence 
      select accseq.Concat(new[] {item})); 
}

Using this, you can implement your method like this:

static IEnumerable<string> GetAllPossibleCombinations(
    int lengthofeachintreturnedinarray, 
    IEnumerable<string> typesofelementsusedincombinations) 
{
    return Enumerable
        .Repeat(typesofelementsusedincombinations, lengthofeachintreturnedinarray)
        .CartesianProduct()
        .Select(strings => String.Concat(strings));
}

all possible combinations between certain amount of digits c#

1 Answers