随机生成100个字母ABCD
其中50个A  30个B 10个C  10个D
有没有好点的方法

1 先随机生成呗，一边生成，一边检测，比如D已经10个了，就改为随机生成ABC，以此类推就可以了。
2 先全部生成，完了以后再检测，多了的就去掉，然后继续，直到满足要求。
3 先按要求弄50个A，30个B，10个C，10个D出来，然后随机抽取排序。（这个方法好像有点走歪了的感觉）

        static void Main(string[] args)
        {
            const string cntA = "A";
            const string cntB = "B";
            const string cntC = "C";
            const string cntD = "D";
            int intA = 50;
            int intB = 30;
            int intC = 10;
            int intD = 10;

            string[] strArr = new string[4] { cntA, cntB, cntC, cntD };
            int[] intCount = new int[4] { 0, 0, 0, 0 };
            Random ran = new Random();

            while (intCount[0] < intA || intCount[1] < intB || intCount[2] < intC || intCount[3] < intD)
            {
                int intIndex = ran.Next(0, 4);
                string strCur = strArr[intIndex];
                switch (strCur)
                {
                    case cntA:
                        if (intCount[0] < intA)
                        {
                            intCount[0]++;
                            Console.Write(strCur);
                        }
                        break;
                    case cntB:
                        if (intCount[1] < intB)
                        {
                            intCount[1]++;
                            Console.Write(strCur);
                        }
                        break;
                    case cntC:
                        if (intCount[2] < intC)
                        {
                            intCount[2]++;
                            Console.Write(strCur);
                        }
                        break;
                    case cntD:
                        if (intCount[3] < intD)
                        {
                            intCount[3]++;
                            Console.Write(strCur);
                        }
                        break;
                    default:
                        break;
                }
            }

            Console.WriteLine("随机生成完成!");
            Console.WriteLine("A的总数:{0}", intCount[0]);
            Console.WriteLine("B的总数:{0}", intCount[1]);
            Console.WriteLine("C的总数:{0}", intCount[2]);
            Console.WriteLine("D的总数:{0}", intCount[3]);
        }