统计硬币 的组合问题

Problem Description
假设一堆由1分、2分、5分组成的n个硬币总面值为m分，求一共有多少种可能的组合方式（某种面值的硬币可以数量可以为0）。

Input
输入数据第一行有一个正整数T，表示有T组测试数据；
接下来的T行，每行有两个数n,m，n和m的含义同上。

Output
对于每组测试数据，请输出可能的组合方式数；
每组输出占一行。

Sample Input
2
3 5
4 8

Sample Output
1
2

 static void Main(string[] args)
        {
            int m = 12;
            string[] arr = { "1", "2", "5" };
            int maxlen = m / 1;
            int mixlen = m / 5;
            for (int i = mixlen; i <= maxlen; i++)
            {
                StringCollection stringCollection = MakeStrings(arr, i);
                foreach (var item in stringCollection)
                {
                    int sum = 0;
                    char[] strarr = item.ToArray();
                    foreach (char item2 in strarr)
                    {
                        sum += Convert.ToInt32(item2 - 48);
                    }
                    if (sum == m)
                    {
                        Console.WriteLine(item);
                    }
                }           
            }
            Console.ReadLine();
        }


        static StringCollection MakeStrings(string[] characters, int finalStringLength)
        {
            int finalLength = finalStringLength; // The length of the final strings.
            StringCollection existingStrings;
            StringCollection newStrings = new StringCollection(); // Start with the all one-letter combinations.

            newStrings.AddRange(characters);

            for (int len = 2; len <= finalLength; len++)
            {
                // Start a new collection of strings based on the existing strings.
                existingStrings = newStrings;
                newStrings = new StringCollection();

                // Concatenate every string of length (len-1)...
                foreach (string str in existingStrings)
                {
                    // ...with every character...
                    foreach (string ch in characters)
                    {
                        // ...to create every possible string of length len.
                        newStrings.Add(str + ch);
                    }
                }
            }
            return newStrings;
        }