成语接龙，哈希表神马的最给力了。

  
    

   
     using
   
      System;

   
     using
   
      System.Collections.Generic;

   
     using
   
      System.IO;

   
     using
   
      System.Text;


   
     namespace
   
      ConsoleApplication1
{
 
   
     public
   
      
   
     class
   
      Idiom
 {
 
   
     public
   
      
   
     static
   
      Dictionary
   
     <
   
     Char, List
   
     <
   
     int
   
     >>
   
      Dict 
   
     =
   
      
   
     new
   
      Dictionary
   
     <
   
     char
   
     , List
   
     <
   
     int
   
     >>
   
     ();
 
   
     public
   
      
   
     static
   
      List
   
     <
   
     Idiom
   
     >
   
      IdiomList 
   
     =
   
      
   
     new
   
      List
   
     <
   
     Idiom
   
     >
   
     ();
 
   
     static
   
      Idiom()
 {
 
   
     string
   
     [] Arr
   
     =
   
      File.ReadAllLines(Environment.CurrentDirectory 
   
     +
   
      
   
     @"
   
     \idiom.txt
   
     "
   
     ,Encoding.UTF8);
 
   
     for
   
      (
   
     int
   
      i 
   
     =
   
      
   
     0
   
     ; i 
   
     <
   
      Arr.Length; i
   
     ++
   
     )
 {
 Idiom I 
   
     =
   
      
   
     new
   
      Idiom(i, Arr[i]);
 IdiomList.Add(I);
 
   
     if
   
      (
   
     !
   
     Dict.ContainsKey(I.Head))
 {
 Dict.Add(I.Head, 
   
     new
   
      List
   
     <
   
     int
   
     >
   
     ());
 }
 Dict[I.Head].Add(I.ID);
 }
 }
 
   
     public
   
      Idiom(
   
     int
   
      id,
   
     string
   
      word )
 {
 ID 
   
     =
   
      id;
 Word 
   
     =
   
      word;
 
   
     char
   
     [] C 
   
     =
   
      word.ToCharArray();
 Head 
   
     =
   
      C[
   
     0
   
     ];
 Tail 
   
     =
   
      C[word.Length 
   
     -
   
      
   
     1
   
     ];
 }
 
   
     public
   
      
   
     string
   
      Word;
 
   
     public
   
      
   
     int
   
      ID;
 
   
     public
   
      
   
     char
   
      Tail;
 
   
     public
   
      
   
     char
   
      Head;
 }
}
  
    

  
    

   
     using
   
      System;

   
     using
   
      System.Collections.Generic;

   
     using
   
      System.Linq;

   
     using
   
      System.Text;


   
     namespace
   
      ConsoleApplication1
{
 
   
     public
   
      
   
     class
   
      Dragon
 {
 
   
     public
   
      Dragon(Idiom I )
 {
 Body.Add(I.ID);
 Tail 
   
     =
   
      I.Tail;
 }
 
   
     public
   
      Dragon(Dragon D, Idiom I)
 {
 Body 
   
     =
   
      
   
     new
   
      HashSet
   
     <
   
     int
   
     >
   
     (D.Body);
 Body.Add(I.ID);
 Tail 
   
     =
   
      I.Tail;
 }
 
   
     public
   
      HashSet
   
     <
   
     int
   
     >
   
      Body 
   
     =
   
      
   
     new
   
      HashSet
   
     <
   
     int
   
     >
   
     ();
 
   
     public
   
      Char Tail{
   
     get
   
     ;
   
     set
   
     ;} 
 }
}
  
    

  
    

   
     using
   
      System;

   
     using
   
      System.Collections.Generic;

   
     using
   
      System.Linq;

   
     using
   
      System.Text;

   
     using
   
      System.Diagnostics;

   
     using
   
      System.IO;


   
     namespace
   
      ConsoleApplication1
{
 
   
     class
   
      Program
 {

 
   
     static
   
      Stopwatch SW 
   
     =
   
      
   
     new
   
      Stopwatch();
 
   
     static
   
      
   
     bool
   
      Finish 
   
     =
   
      
   
     true
   
     ; 
 
   
     static
   
      Dragon maxDragon 
   
     =
   
      
   
     null
   
     ;
 
   
     static
   
      
   
     int
   
      maxLength 
   
     =
   
      
   
     1
   
     ;
 
   
     static
   
      
   
     void
   
      Main(
   
     string
   
     [] args)
 {
 SW.Start();
 
   
     char
   
      input 
   
     =
   
      
   
     '
   
     三
   
     '
   
     ;
 
   
     if
   
      (Idiom.Dict.ContainsKey(input))
 {
 List
   
     <
   
     int
   
     >
   
      First 
   
     =
   
      Idiom.Dict[input];
 
   
     foreach
   
      (
   
     int
   
      i 
   
     in
   
      First)
 {
 Dragon D 
   
     =
   
      
   
     new
   
      Dragon(Idiom.IdiomList[i]);
 
   
     if
   
      (Finish) { maxDragon 
   
     =
   
      D; Finish 
   
     =
   
      
   
     false
   
     ; }
 DFS(D);
 }
 }
 
   
     else
   
     
 {
 Console.WriteLine(
   
     "
   
     输入的词不存在
   
     "
   
     );
 }

 Console.Read();
 }

 
   
     private
   
      
   
     static
   
      
   
     void
   
      DFS(Dragon D)
 {
 
 
   
     if
   
      (SW.ElapsedMilliseconds 
   
     >
   
      
   
     1000
   
      
   
     &&
   
      
   
     !
   
     Finish)
 {
 SW.Stop();
 
 
   
     if
   
      (maxDragon.Body.Count 
   
     ==
   
      maxLength)
 {
 
   
     foreach
   
      (
   
     int
   
      i 
   
     in
   
      maxDragon.Body)
 {
 Console.Write(Idiom.IdiomList[i].Word 
   
     +
   
      
   
     "
   
     ,
   
     "
   
     );
 }
 Console.WriteLine(maxDragon.Body.Count);
 }
 
 Finish 
   
     =
   
      
   
     true
   
     ;
 
   
     return
   
     ;
 }
 
   
     if
   
      (Finish) { 
   
     return
   
     ; } 
 
   
     if
   
      (Idiom.Dict.ContainsKey(D.Tail))
 {
 
   
     foreach
   
      (
   
     int
   
      i 
   
     in
   
      Idiom.Dict[D.Tail])
 {
 
   
     if
   
      (
   
     !
   
     D.Body.Contains(i))
   
     //
   
     无环
   
     

   
      {
 Dragon newDragon 
   
     =
   
      
   
     new
   
      Dragon(D, Idiom.IdiomList[i]);
 
   
     if
   
      (newDragon.Body.Count 
   
     >
   
      maxDragon.Body.Count)
 {
 maxDragon 
   
     =
   
      newDragon;
 maxLength
   
     =
   
     newDragon.Body.Count;
 }
 DFS(newDragon);
 }
 }
 }
 }
 }
}