超难问题，求解决方法！

Question

如：A,B,C(顺序)，求不同的组合形式如下
A
B
C
AB
AC
BC
ABC
以上是三个字母的各种组合形式，那如果是N个如何用程序实现？

Answer 1

        static void Main(string[] args)
        {
            string[] arr = new[] { "A", "B", "C", "D", "E" };
            GetCombination(arr);
        }        static void GetCombination(string[] nums)
        {
            double count = Math.Pow(2, nums.Length);
            for (int i = 1; i <= count - 1; i++)
            {
                string str = Convert.ToString(i, 2).PadLeft(nums.Length, '0');
                for (int j = 0; j < str.Length; j++)
                {
                    if (str[j] == '1')
                    {
                        Console.Write(nums[j]);
                    }
                }
                Console.WriteLine();
            }
        }
/*
输出:
E
D
DE
C
CE
CD
CDE
B
BE
BD
BDE
BC
BCE
BCD
BCDE
A
AE
AD
ADE
AC
ACE
ACD
ACDE
AB
ABE
ABD
ABDE
ABC
ABCE
ABCD
ABCDE
*/
http://topic.csdn.net/u/20090217/21/f41ed9f6-f929-451c-a5c9-80d2e408422a.html?70689

Answer 2

随便写了一个，有点啰嗦，自己改进吧using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;namespace Test_CSharp_Console
{
    class Program
    {
        static char[] c = { 'A', 'B', 'C' };
        static void Main(string[] args)
        {            ShowArr(1);        }        static void ShowArr(int i)
        {
            
            int k, m, n;
            for (k = 0; k < 3; k++)
            {
                if (i == 1)
                {
                    Console.WriteLine(c[k]);
                    continue;
                }
                for (m = 0; m < 3; m++)
                {
                    if (i == 2)
                    {
                        Console.WriteLine(c[k].ToString() + c[m].ToString());
                        continue;
                    }
                    for (n = 0; n < 3; n++)
                    {
                        if (i == 3)
                        {
                            Console.WriteLine(c[k].ToString() + c[m].ToString() + c[n].ToString());
                            continue;
                        }
                    }
                }               
                
            }
            i++;
            if (i > 3) return;
            ShowArr(i);
        }
    }
}

Answer 3

返回结果如下A
B
C
AA
AB
AC
BA
BB
BC
CA
CB
CC
AAA
AAB
AAC
ABA
ABB
ABC
ACA
ACB
ACC
BAA
BAB
BAC
BBA
BBB
BBC
BCA
BCB
BCC
CAA
CAB
CAC
CBA
CBB
CBC
CCA
CCB
CCC

Answer 4

用迭代实现的，思想其实很简单
你如果得到了ABC的所有组合，再得到ABCD的组合就很简单了，将D添加到ABC所有可能的组合里面，并添加一个单独的D
        static void Main(string[] args)
        {
            string str ="ABCD";
            List<char> input = new List<char>(str.ToCharArray());
            List<string> result = new List<string>();
            GetAllCombination(input, result);            foreach (string s in result)
                Console.WriteLine(s);
        }        static void GetAllCombination(List<char> elements, List<string> combinations)
        {
            if (elements.Count == 0) return;
            char lastChar = elements[elements.Count - 1];
            elements.RemoveAt(elements.Count - 1);
            GetAllCombination(elements, combinations);
            List<string> copy = new List<string>(combinations.ToArray());
            foreach (string str in copy)
                combinations.Add(str + lastChar);
            combinations.Add(lastChar.ToString());
        }