调试易

对每一个char循环，递归得到这个char开头的子串

就常规的两个循环，如果还去除重复的子串则稍稍麻烦一点string s = "hello";
for (int i = 0; i < s.Length; i++)
{
    for (int length = 1; length < s.Length-i+1; length++)
    {
        Console.WriteLine( s.Substring(i, length) );
    }
}

sorry，前面的回复“全排列去掉自身”可能不对
排列组合是高中学的，时间太长都不记得了~

你说的对。
被楼主用子串误导了。string s = "ABCD";
int combination = 1 << s.Length;for (int i = 1; i < combination - 1; i++)
{
    for (int j = 0; j < s.Length; j++)
    {
        if( (i >> j) % 2 == 1 )Console.Write( s[j] );
    }
    Console.WriteLine();
}

按lz的需求写了个：public class PermutationCombination
    {
        /// <summary>
        /// 显示一个字符串的排列组合
        /// 
        /// 主要思路就是：譬如字符串"ABCD"
        /// 新添                                    已有                                结果
        /// "D"
        /// "C","CD"                                "D"                                 "C","CD","D"
        /// "B","BC","BCD", "BD"                    "C","CD","D"                        "B","BC","BCD","BD","C","CD","D"
        /// "A","AB","ABC","ABCD","AC","ACD","AD"   "B","BC","BCD","BD","C","CD","D"    "A","AB","ABC","ABCD","AC","ACD","AD","B","BC","BCD","BD","C","CD","D" 
        /// </summary>
        /// <param name="str">字符串</param>
        /// <param name="results">存放组合的子串</param>
        /// <param name="pos">添加字符串的位置</param>
        public static void Show(string str, List<string> results, int pos)
        {
            if (string.IsNullOrEmpty(str))
                return;
            List<string> newResults = new List<string>();
            
            newResults.Add(str[pos].ToString());
            if (pos != str.Length - 1)
            {
                foreach (string s in results)
                {
                    newResults.Add(str[pos].ToString() + s);
                    
                }
                foreach (string s in results)
                {
                    newResults.Add(s);
                }
                
            }
            results.Clear();
            results = newResults;
            if (pos > 0)
            {
                Show(str, results, pos - 1);
            }
            else if (pos == 0)
            {
                foreach (string s in results)
                {
                    Console.WriteLine(s);
                }
            }        }        public static void Main(String[] args)
        {
            List<string> results = new List<string>();
            string str = "ABCD";
            PermutationCombination.Show(str, results, str.Length - 1);
        }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Collections;
namespace 排列
{
    class 排列
    {
        System.Collections.ArrayList a = new System.Collections.ArrayList();
        public 排列(string 字符串)
        {
            递归求子串(字符串);
            a.RemoveAt(a.IndexOf(字符串));
            a.Sort();
            //以下为循环移除相同的项!
            for (int i = 1; i < a.Count; i++)
            {
                if (a[i].Equals(a[i-1]))
                {
                    a.RemoveAt(i);
                    i--;
                }
            }
            PrintIndexAndValues(a);
        }
        public static void PrintIndexAndValues(IEnumerable myList)
        {
            int i = 0;
            foreach (Object obj in myList)
                Console.WriteLine("\t[{0}]:\t{1}", i++, obj);
            Console.WriteLine();
        }        //以下为递归方法,把C字符传所有少一个字符的子串全部加入ArrayList
        //以下递归方法的出口为,字符传的长度等于1
        private void 递归求子串(string c)
        {
            if (c.Length == 1)
            {
                a.Add(c);
            }
            else
            {
                a.Add(c);
                for (int i = 0; i < c.Length; i++)
                {
                    string c1 = c.Remove(i, 1);
                    递归求子串(c1);
                }
            }
        }
    }
}