Problem:
Enumeration of Subsets III

You are given a set $T$, which is a subset of $S$. The set $S$ consists of $0, 1, ... n-1$.

Print all subsets of $T$.

Note that we represent $0, 1, ... n-1$ as 00...0001, 00...0010, 00...0100, ..., 10...0000 in binary respectively and the integer representation of a subset is calculated by bitwise OR of existing elements.

Input

The input is given in the following format.

$n$
$k \; b_0 \; b_1 \; ... \; b_{k-1}$

$k$ is the number of elements in $T$, and $b_i$ represents elements in $T$.

Output

Print the subsets ordered by their decimal integers. Print a subset in the following format.

$d$: $e_0$ $e_1$ ...

Print ':' after the integer value $d$, then print elements $e_i$ in the subset in ascending order. Separate two adjacency elements by a space character.

Constraints

$1 \leq n \leq 28$

$0 \leq k \leq 18$

$k \leq n$

$0 \leq b_i < n$

Sample Input 1

4
2 0 2

Sample Output 1

0:
1: 0
4: 2
5: 0 2

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ITP2_11_C
{
    public class Program

    {

        public static void Main(string[] args)
        {
            int n = ReadInt();
            List<int> s;

            int partialSet = 0;
            foreach (var x in ReadIntAr().Skip(1)) partialSet |= (1 << x);

            for (int i = 0 ; i < (1 << n) ; i++)
            {
                if ((i | partialSet) == partialSet)
                {
                    s = new List<int>(n);
                    for (int j = 0 ; j < n ; j++)
                    {
                        if ((i >> j & 1) == 1) s.Add(j);
                    }
                    Console.WriteLine("{0}:{1}", i, (s.Count == 0 ? "" : " ") + string.Join(" ", s.Select(x => x.ToString()).ToArray()));
                }
            }
        }

        static string ReadSt() { return Console.ReadLine(); }
        static int ReadInt() { return int.Parse(Console.ReadLine()); }
        static long ReadLong() { return long.Parse(Console.ReadLine()); }
        static double ReadDouble() { return double.Parse(Console.ReadLine()); }
        static string[] ReadStAr(char sep = ' ') { return Console.ReadLine().Split(sep); }
        static int[] ReadIntAr(char sep = ' ') { return Array.ConvertAll(Console.ReadLine().Split(sep), e => int.Parse(e)); }
        static long[] ReadLongAr(char sep = ' ') { return Array.ConvertAll(Console.ReadLine().Split(sep), e => long.Parse(e)); }
        static double[] ReadDoubleAr(char sep = ' ') { return Array.ConvertAll(Console.ReadLine().Split(sep), e => double.Parse(e)); }
        static string WriteAr(int[] array, string sep = " ") { return String.Join(sep, array.Select(x => x.ToString()).ToArray()); }
        static string WriteAr(double[] array, string sep = " ") { return String.Join(sep, array.Select(x => x.ToString()).ToArray()); }
        static string WriteAr(long[] array, string sep = " ") { return String.Join(sep, array.Select(x => x.ToString()).ToArray()); }

    }

}