使用枚举器求索引的全排列

[hmlb1981]

caozhy使用枚举器求索引的全排列是个好办法，学习了一下，重新写了一个函数。

/// <summary>
/// 使用枚举器生成[n, count)索引全排列 。
/// </summary>
/// <param name="count">数目，索引在[0, count - 1]间 。</param>
/// <returns>索引全排列 。</returns>
/// <exception cref="ArgumentOutOfRangeException">如果count非法，抛出ArgumentOutOfRangeException 。</exception>
public static IEnumerable<IList<int>> PermutationIndice(int count)
{
if (count < 0)
{
throw new ArgumentOutOfRangeException("count");
}

IEnumerable<int> allIndice = Enumerable.Range(0, count);
IEnumerable<IList<int>> permutation = null;
for (int i = 0; i < count; i++)
{ // 每次迭代，求i个索引的排列全集
if (i == 0)
{
permutation = Enumerable.Select<int, IList<int>>(allIndice, x => new int[] { x });
//permutation = allIndice.Select<IList<int>>(x => new int[] { x });
}
else
{
permutation = Enumerable.SelectMany<IList<int>, IList<int>>(permutation,
l => Enumerable.Select<int, IList<int>>(allIndice.Except(l), x => new List<int>(l).Concat(new int[] { x }).ToList()));
//l => allIndice.Except(l).SelectMany<IList<int>>(x => new List<int>(new List<int>(l).Concat(new int[] { x}).ToList())));
}
}

return permutation;
}

[threenewbee]

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var result = Arrange(4);
            foreach (var item in result)
            {
                Console.WriteLine(string.Join(",", item.Select(x => x.ToString()).ToArray()));
            }
        }

        static IEnumerable<IEnumerable<int>> Arrange(int n)
        {
            IEnumerable<IEnumerable<int>> result = Enumerable.Range(0, n).Select(x => new List<int>() { x });
            while (result.First().Count() < n)
            {
                result = result.SelectMany(x => Enumerable.Range(0, n).Except(x).Select(y => x.Concat(new List<int>() { y })));
            }
            return result;
        }
    }
}

这样？

[hmlb1981]

是的，但是程序里没有注释，因此花了一些时间理解思路。

[threenewbee]

顺便贴一个递归版本的：

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var result = Arrange(4);
            foreach (var item in result)
            {
                Console.WriteLine(string.Join(",", item.Select(x => x.ToString()).ToArray()));
            }
        }

        static IEnumerable<IEnumerable<int>> Arrange(int n, IEnumerable<IEnumerable<int>> seed = null)
        {
            if (seed == null)
                seed = Enumerable.Range(0, n).Select(x => new List<int>() { x });
            if (seed.First().Count() == n) return seed;
            return Arrange(n, seed.SelectMany(x => Enumerable.Range(0, n).Except(x).Select(y => x.Concat(new List<int>() { y }))));
        }
    }
}

[threenewbee]

用yield return展开：

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var result = Arrange(4);
            foreach (var item in result)
            {
                Console.WriteLine(string.Join(",", item.Select(x => x.ToString()).ToArray()));
            }
        }

        static IEnumerable<IEnumerable<int>> Arrange(int n, IEnumerable<IEnumerable<int>> seed = null)
        {
            if (seed == null)
                seed = Enumerable.Range(0, n).Select(x => new List<int>() { x });
            if (seed.First().Count() == n)
            {
                foreach (var item in seed) 
                    yield return item;
            }
            else
            {
                foreach (var item in Arrange(n, seed.SelectMany(x => Enumerable.Range(0, n).Except(x).Select(y => x.Concat(new List<int>() { y })))))
                    yield return item;
            }
        }
    }
}

[寂小魔]

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] charString = { "L", "O", "V", "E" };
            for (int i = 0; i < Total.Count; i++)
            {
                Console.WriteLine(Total[i]);
            }
            Console.ReadKey();
        }


        List<string> Total = new List<string>();
        /// <summary>
        /// 全排列
        /// </summary>
        /// <param name="charString">排列源字符</param>
        /// <param name="count">排列数目</param>
        /// <param name="str"></param>
        public void test(string[] charString, int count, string str="")
        {
            foreach (string wd in charString)
            {
                string newStr = str + wd;
                if (newStr.Length > count-1)
                {
                    Total.Add(newStr);
                }
                else
                {
                    test(charString, count, newStr);
                }
            }
        }
    }
}

. . 抄袭加改造。这个算不算 . .