1+
2+ using System ;
3+ using System . Collections . Generic ;
4+ using System . Linq ;
5+ using System . Text ;
6+ using System . Threading . Tasks ;
7+ 8+ namespace _126WordLadderII_P1
9+ {
10+ /// <summary>
11+ /// Leetcode 126: Word ladder II
12+ /// code review on July 9, 2018
13+ /// </summary>
14+ class Program
15+ {
16+ static void Main ( string [ ] args )
17+ {
18+ string beginWord = "hit" ;
19+ string endWord = "cog" ;
20+ var words = new string [ 5 ] { "hot" , "dot" , "dog" , "lot" , "log" } ;
21+ var wordList = new HashSet < string > ( words ) ;
22+ 23+ var result = FindLadders ( beginWord , endWord , wordList ) ;
24+ }
25+ 26+ private static List < List < String > > Ladders = new List < List < string > > ( ) ;
27+ private static List < String > Words = new List < string > ( ) ;
28+ 29+ public static List < List < String > > FindLadders (
30+ String beginWord ,
31+ String endWord ,
32+ ISet < String > wordList ) {
33+ 34+ var ladders = new List < List < string > > ( ) ;
35+ 36+ if ( beginWord . CompareTo ( endWord ) == 0 ) {
37+ var words = new List < string > ( ) ;
38+ 39+ words . Add ( beginWord ) ;
40+ ladders . Add ( words ) ;
41+ return ladders ;
42+ }
43+ 44+ var dict = new HashSet < string > ( ) ;
45+ 46+ dict = new HashSet < string > ( wordList ) ;
47+ dict . Add ( endWord ) ;
48+ 49+ var dictionary = new Dictionary < String , int > ( ) ;
50+ int dist = getLadderLengthAndDictionary ( beginWord , endWord , dict , dictionary ) ;
51+ 52+ var keys = new List < string > ( dictionary . Keys ) ;
53+ foreach ( string key in keys )
54+ {
55+ dictionary [ key ] = dist - 1 - dictionary [ key ] ;
56+ }
57+ 58+ var visited = new HashSet < string > ( ) ;
59+ 60+ getLadders ( dist - 1 , beginWord , endWord , dict , visited , dictionary ) ;
61+ 62+ return ladders ;
63+ }
64+ 65+ /// <summary>
66+ ///
67+ /// </summary>
68+ /// <param name="beginWord"></param>
69+ /// <param name="endWord"></param>
70+ /// <param name="wordList"></param>
71+ /// <param name="ladderDictionary"></param>
72+ /// <returns></returns>
73+ private static int getLadderLengthAndDictionary (
74+ String beginWord ,
75+ String endWord ,
76+ ISet < String > wordList ,
77+ Dictionary < String , int > ladderDictionary )
78+ {
79+ int length = 0 ;
80+ 81+ var visited = new HashSet < string > ( ) ;
82+ 83+ var queue = new Queue < string > ( ) ;
84+ var queueDist = new Queue < int > ( ) ;
85+ 86+ queue . Enqueue ( beginWord ) ;
87+ 88+ queueDist . Enqueue ( 0 ) ;
89+ 90+ visited . Add ( beginWord ) ;
91+ 92+ while ( queue . Count > 0 ) {
93+ 94+ var word = queue . Dequeue ( ) ;
95+ int len = queueDist . Dequeue ( ) ;
96+ 97+ ladderDictionary [ word ] = len ;
98+ 99+ if ( word . CompareTo ( endWord ) == 0 ) {
100+ length = len + 1 ;
101+ break ;
102+ }
103+ 104+ // get all neighbors of w, and add them to the queue,
105+ // if they have not been visited.
106+ for ( int i = 0 ; i < word . Length ; ++ i ) {
107+ for ( int iterate = 'a' ; iterate <= 'z' ; ++ iterate ) {
108+ var characters = word . ToCharArray ( ) ;
109+ 110+ if ( iterate != characters [ i ] ) {
111+ characters [ i ] = ( char ) iterate ; // don't forget type conversion.
112+ var current = new String ( characters ) ;
113+ 114+ if ( wordList . Contains ( current ) && ! visited . Contains ( current ) ) {
115+ queue . Enqueue ( current ) ;
116+ 117+ queueDist . Enqueue ( len + 1 ) ;
118+ 119+ visited . Add ( current ) ;
120+ }
121+ }
122+ }
123+ }
124+ }
125+ 126+ return length ;
127+ }
128+ 129+ /// <summary>
130+ /// code review on July 9, 2018
131+ /// </summary>
132+ /// <param name="dist"></param>
133+ /// <param name="word"></param>
134+ /// <param name="endWord"></param>
135+ /// <param name="dict"></param>
136+ /// <param name="visited"></param>
137+ /// <param name="ladderDictionary"></param>
138+ private static void getLadders (
139+ int dist ,
140+ String word ,
141+ String endWord ,
142+ ISet < String > dict ,
143+ ISet < String > visited ,
144+ Dictionary < String , int > ladderDictionary )
145+ {
146+ visited . Add ( word ) ;
147+ Words . Add ( word ) ;
148+ 149+ if ( word . CompareTo ( endWord ) == 0 ) {
150+ var list = new List < string > ( ) ;
151+ 152+ list . AddRange ( Words ) ;
153+ Ladders . Add ( list ) ;
154+ }
155+ else if ( dist == 0 || ladderDictionary [ word ] > dist ) {
156+ // do nothing.
157+ }
158+ else
159+ {
160+ var characters = word . ToCharArray ( ) ;
161+ 162+ for ( int i = 0 ; i < word . Length ; ++ i ) {
163+ var current = characters [ i ] ;
164+ var currentChar = word [ i ] ;
165+ 166+ for ( int iterate = 'a' ; iterate <= 'z' ; ++ iterate ) {
167+ if ( iterate != currentChar )
168+ {
169+ characters [ i ] = ( char ) iterate ;
170+ var currentWord = new String ( characters ) ;
171+ 172+ if ( dict . Contains ( currentWord ) && ! visited . Contains ( currentWord ) ) {
173+ getLadders ( dist - 1 , currentWord , endWord , dict , visited , ladderDictionary ) ;
174+ }
175+ }
176+ }
177+ 178+ characters [ i ] = current ; // restore.
179+ }
180+ }
181+ 182+ visited . Remove ( word ) ;
183+ Words . RemoveAt ( Words . Count - 1 ) ;
184+ }
185+ }
186+ }
187+
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