Generating power set recursively without any loops

Question

How do you write a recursive method PowerSet(String input) that prints out all possible combinations of a string that is passed to it?

For example: PowerSet(\"abc\")

Answer 1

Based on the info here, here is solution in C#.

NOTE: the loop in the main function is just to print the result into the console value. No loops used in the PowerSet method.

    public static void Main(string[] args)
    {

        string input = "abbcdd";


        Dictionary < string, string> resultSet = new Dictionary();

        PowerSet(input, "", 0, resultSet);

        //apply sorting 
        var resultSorted = resultSet.OrderBy(l => l.Key.Length).ThenBy(l=>l.Key);

        //print values
        foreach(var keyValue in resultSorted)
        {
            Console.Write("{{{0}}}, ",keyValue.Key);
        }


    }

    /// 

    /// Computes the powerset of a string recursively
    /// based on the Algorithm http://www.ideserve.co.in/learn/generate-all-subsets-of-a-set-recursion
    /// 
    /// Original input string
    /// Temporary variable to store the current char for the curr call
    /// The character position we are evaluating to add to the set
    /// A hash list to store the result
    public static void PowerSet(string input, string temp, int depth, Dictionary resultSet)
    {

        //base case
        if(input.Length == depth)
        {
            //remove duplicate characters
            string key = new string(temp.ToCharArray().Distinct().ToArray());

            //if the character/combination is already in the result, skip it
            if (!resultSet.ContainsKey(key))
                resultSet.Add(key, key);

            return;//exit 
        }

        //left
        PowerSet(input, temp, depth + 1, resultSet);

        //right
        PowerSet(input, temp + input[depth], depth + 1, resultSet);

    }