递归法求解数列组合的各种情况

C#代码：

        static void Main(string[] args)
        {
            int[] items = new int[] { 0,1,2,3,4};
            int m = 3;
            List<int[]> allCombinations = GetCombinations(items, m);
            foreach (int[] combination in allCombinations)
            {
                Console.WriteLine(string.Join(",", combination));
            }
        }
        static List<int[]> GetCombinations(int[] items, int m)
        {
            List<int[]> allCombinations = new List<int[]>();
            int[] combination = new int[m];
            GetCombinations(items, m, 0, combination, 0, allCombinations);
            return allCombinations;
        }

        static void GetCombinations(int[] items, int m, int itemIndex, int[] combination, int combinationIndex, List<int[]> allCombinations)
        {
            if (combinationIndex == m)
            {
                allCombinations.Add((int[])combination.Clone());
                return;
            }
            if (itemIndex >= items.Length)
            {
                return;
            }
            combination[combinationIndex] = items[itemIndex];
            GetCombinations(items, m, itemIndex + 1, combination, combinationIndex + 1, allCombinations);
            GetCombinations(items, m, itemIndex + 1, combination, combinationIndex, allCombinations);
        }

图解：