作者： 吴杰

C#合并数组

public string[] MergerArray(string[] First, string[] Second)
{
    string[] result = new string[First.Length + Second.Length];
    First.CopyTo(result, 0);
    Second.CopyTo(result, First.Length);
    return result;
}

泛型版本

public T[] MergerArray<T>(T[] First,T[] Second)
{
    T[] result =new T[First.Length + Second.Length];
    First.CopyTo(result, 0);
    Second.CopyTo(result, First.Length);
    return result;
}

合并多个数组

/// <summary>
/// 连接多个数组
/// </summary>
/// <typeparam name="T">数组数据类型</typeparam>
/// <param name="source">源数组</param>
/// <param name="arrays">被连接的多个数组</param>
/// <returns></returns>
public static T[] Concat<T>(this T[] source, params T[][] arrays)
{
    if (source == null)
    {
        throw new ArgumentNullException("source");
    }


    var length = source.Length + arrays.Sum(array => array != null ? array.Length : 0);
    var result = new T[length];
    length = source.Length;
    Array.Copy(source, 0, result, 0, source.Length);
    foreach (var array in arrays)
    {
        if (array != null)
        {
            Array.Copy(array, 0, result, length, array.Length);
            length += array.Length;
        }
    }
    return result;
}

C# 生成允许重复的排列、组合

/// <summary>
/// 获取允许重复的排列组合
/// </summary>
/// <param name="s"> 源字符串</param>
/// <param name="cnt"> 组合位数</param>
/// <returns> 生成结果</returns>
static IEnumerable<string > GetVariations(string s)
{
        int[] indexes = new int[s.Length];
        StringBuilder sb = new StringBuilder ();

        while (IncrementIndexes(indexes, s.Length))
        {
            sb.Clear();
            for ( int i = 0; i < indexes.Length; i++)
            {
                    if (indexes[i] != 0)
                    {
                            sb.Append(s[indexes[i] - 1]);
                    }
            }

            yield return sb.ToString();

        }
}

static bool IncrementIndexes( int[] indexes, int limit)
{
        for ( int i = 0; i < indexes.Length; i++)
        {
            indexes[i]++;
            if (indexes[i] > limit)
            {
                    indexes[i] = 1;
            }
            else
            {
                    return true;
            }
        }
        return false;
}

排列 和 组合的区别

排列是有顺序的，如（a，b，c）和（b，c，a）是不同的，虽然同样是三个字母，但顺序不同。

组合是没有顺序的，如（a，b，c）和（b，c，a）是相同的，只要是同样的字母组合，顺序无所谓。

C# 随机生成字符串

/// <summary>
/// 生成随机纯字母组合
/// </summary>
/// <param name="count"> 位数</param>
/// <returns> 随机码</returns>
private string GetRandomString( int count)
{
        int number;
        string checkCode = String.Empty;     //存放随机码的字符串  

        System. Random random = new Random( DateTime.Now.Millisecond * 2);

        for ( int i = 0; i < count; i++) //产生4位校验码  
        {
            number = random.Next();
            number = number % 36;
            if (number < 10)
            {
                    number += 48;    //数字0-9编码在48-57  
            }
            else
            {
                    number += 55;    //字母A-Z编码在65-90  
            }

            checkCode += (( char)number).ToString();
        }
        return checkCode;
}

/// <summary>
/// 按位数取得随机码(纯数字)
/// </summary>
/// <param name="num"> 位数</param>
/// <returns> 随机码</returns>
public string GetRandomNumber( int num)
{
        string str = "";
        int seed = Math.Abs((int )BitConverter .ToUInt32(Guid.NewGuid().ToByteArray(), 0));
        Random random = new Random(seed);

        for ( int i = 0; i < num; i++)
        {
            str += random.Next(10);
        }
        return str;
}

/// <summary>
/// 生成随机字母字符串(数字字母混和)
/// </summary>
/// <param name="codeCount"> 待生成的位数 </param>
public string GetRandomCharAndNumber( int codeCount)
{
        
    string str = string.Empty;
    int rep = 0;
    long num2 = DateTime.Now.Ticks + rep;
    rep++;
    Random random = new Random((( int)((( ulong)num2) & 0xffffffffL)) | ((int)(num2 >> rep)));
    for ( int i = 0; i < codeCount; i++)
    {
        char ch;
        int num = random.Next();
        if ((num % 2) == 0)
        {
            ch = ( char)(0x30 + (( ushort)(num % 10)));
        }
        else
        {
            ch = ( char)(0x41 + (( ushort)(num % 0x1a)));
        }
        str = str + ch.ToString();
    }
    return str;
}