All Possible Combinations of a list of Values

Question

I have a list of integers List<int> in my C# program. However, I know the number of items I have in my list only at runtime.

Let us say, for the sake of simplicity, my list is {1, 2, 3} Now I need to generate all possible combinations as follows.

{1, 2, 3} {1, 2} {1, 3} {2, 3} {1} {2} {3} 

Can somebody please help with this?

Answer 1

try this:

static void Main(string[] args) {      GetCombination(new List<int> { 1, 2, 3 }); }  static void GetCombination(List<int> list) {     double count = Math.Pow(2, list.Count);     for (int i = 1; i <= count - 1; i++)     {         string str = Convert.ToString(i, 2).PadLeft(list.Count, '0');         for (int j = 0; j < str.Length; j++)         {             if (str[j] == '1')             {                 Console.Write(list[j]);             }         }         Console.WriteLine();     } } 

Answer 2

Assuming that all items within the initial collection are distinct, we can try using Linq in order to query; let's generalize the solution:

Code:

public static IEnumerable<T[]> Combinations<T>(IEnumerable<T> source) {   if (null == source)     throw new ArgumentNullException(nameof(source));    T[] data = source.ToArray();    return Enumerable     .Range(0, 1 << (data.Length))     .Select(index => data        .Where((v, i) => (index & (1 << i)) != 0)        .ToArray()); } 

Demo:

  var data = new char[] { 'A', 'B', 'C' };    var result = Combinations(data);    foreach (var item in result)     Console.WriteLine($"[{string.Join(", ", item)}]"); 

Outcome:

[] [A] [B] [A, B] [C] [A, C] [B, C] [A, B, C] 

If you want to exclude the initial empty array, put .Range(1, (1 << (data.Length)) - 1) instead of .Range(0, 1 << (data.Length))