一个关于无向图遍历的问题

Question

输入一些二元组，每个表示两个节点之间有一条通路。再输入一个顶点，一个终点，求出一共有多少种走法（不包括回路）。用C#或者Java实现

Answer 1

来个田字格的

 using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string input1 = @"a,b
b,c
a,d
b,e
c,f
d,e
e,f
d,g
e,h
f,i
g,h
h,i";
            foreach (var item in Solve(input1, "", "a", "i"))
                Console.WriteLine(item);
        }

        static IEnumerable<string> Solve(string input, string prepath, string start, string end)
        {
            if (start == end)
            {
                yield return prepath + end;
                yield break;
            }
            var query = input.Split(new string[] { "\r\n" }, StringSplitOptions.RemoveEmptyEntries)
                .Select(x => x.Split(',')[0] + x.Split(',')[1]).Where(x => x.Contains(start) && !prepath.Contains(x.Replace(start, "")));
            foreach (var item in query)
            { 
                foreach (var item1 in Solve(input, prepath + start, item.Replace(start, ""), end))
                    yield return item1;
            }
        }
    }
}