算法复习2(全排序,从M取N个数) *不考虑重复数据

全排序

 static void AllSort(int[] arr, string rtnStr)
        {
            if (arr.Length == 0)
            {
                Console.WriteLine(rtnStr);
                return;
            }

            int i = -1;
            string temp = rtnStr;

            while ((++i) < arr.Length)
            {
                rtnStr = rtnStr + arr[i] + " ";

                int[] rtnArray = GetNextArray(arr, i);
                AllSort(rtnArray, rtnStr);

                rtnStr = temp;
            }
        }

        static int[] GetNextArray(int[] arr, int index)
        {
            int[] rtnArray = arr.Where(p => p != arr[index]).ToArray();

            return rtnArray;
        }

从M个数取N个数

 static void FetchNumN(int[] arr, string rtnStr, int depth, int num)
        {
            if (depth == num)
            {
                Console.WriteLine(rtnStr);
                return;
            }

            int i = -1;
            string tempStr = rtnStr;
            int tempDepth = depth;

            while ((++i) < arr.Length)
            {
                rtnStr = rtnStr + arr[i] + " ";
                depth++;


                int[] rtnArray = GetNextFetchArray(arr, i);
                FetchNumN(rtnArray, rtnStr, depth, num);

                rtnStr = tempStr;
                depth = tempDepth;
            }
        }

        static int[] GetNextFetchArray(int[] arr, int index)
        {
            int[] rtnArray = new int[arr.Length - index - 1];
            int j = -1;
            for (int i = index + 1; i < arr.Length; i++)
            {
                rtnArray[++j] = arr[i];
            }

            return rtnArray;
        }

调用方式

 int[] array = new int[] { 1, 2, 3, 4, 5 };
            AllSort(array, "");
            FetchNumN(array, "", 0, 3);