排列组划算法

排列组合算法
如何计算得到：0~9十个数字选2的 45种排列组合



[解决办法]
IEnumerable<int[]> foo()
{
for (int i = 0; i < 10; i++)
for (int j = i + 1; j < 10; j++)
yield return new int[] { i, j };
}

void Main()
{
foreach (var item in foo())
{
...
}
}
[解决办法]

C# code

for(int i=1;i<=9;i++) for(int j=i+1;j<=9;j++)    Console.WriteLine("{0},{1}",i,j);
[解决办法]

C# code
public static List<string> P(string s)        {            if (s.Length==1)            {                List<string> r = new List<string>();                r.Add("");                r.Add("a");                return r;            }            else            {                List<string> tmp = P(s.Substring(0, s.Length - 1));                List<string> ret=new List<string>();                foreach (string t in tmp)                {                    ret.Add(t);                }                foreach (string t in tmp)                {                    for (int len = t.Length; len >=0; len--)                    {                        string insert = t;                        insert=insert.Insert(len, s[s.Length - 1].ToString());                        ret.Add(insert);                    }                }                return ret;            }        }List<string> ret = P("abcdefghij");            Dictionary<int, string> dic = new Dictionary<int, string>();            foreach (string s in ret)            {                try                {                    dic.Add(s.GetHashCode(), s);                }                catch                {                    MessageBox.Show(s + "_" + dic[s.GetHashCode()]);                }            }