1+ using System . Collections . Generic ;
2+ using System . Runtime . CompilerServices ;
3+
4+ namespace Day_20
5+ {
6+ // 8556
7+ // 8105
8+ // 4439
9+ // 21100 too high
10+
11+ internal class Program
12+ {
13+ static void Main ( string [ ] args )
14+ {
15+ var numbers = File . ReadLines ( "input.txt" ) . Select ( long . Parse ) . Select ( x => x * 811589153 ) . ToArray ( ) ;
16+
17+ Dictionary < long , LinkedListNode < long > > nodeLookup = new ( ) ;
18+ LinkedList < long > linkedList = new ( ) ;
19+
20+
21+ LinkedListNode < long > val0 = null ;
22+
23+ var i = 0 ;
24+ foreach ( var number in numbers )
25+ {
26+ var node = new LinkedListNode < long > ( number ) ;
27+ nodeLookup . Add ( i , node ) ;
28+ linkedList . AddLast ( node ) ;
29+ i ++ ;
30+
31+ if ( number == 0 )
32+ {
33+ val0 = node ;
34+ }
35+ }
36+
37+ Console . WriteLine ( string . Join ( ", " , linkedList ) ) ;
38+ //Console.WriteLine(string.Join(", ", linkedList));
39+
40+ for ( var z = 0 ; z < 10 ; z ++ )
41+ {
42+ for ( var ii = 0 ; ii < linkedList . Count ; ii ++ )
43+ {
44+ Mix ( ii , linkedList , nodeLookup ) ;
45+ //Console.WriteLine(string.Join(", ", linkedList));
46+ }
47+ }
48+
49+ Console . WriteLine ( string . Join ( ", " , linkedList ) ) ;
50+ Console . WriteLine ( "finish" ) ;
51+
52+
53+
54+ var iterator = val0 ;
55+ var sum = 0l ;
56+ for ( long z = 0 ; z < 3 ; z ++ )
57+ {
58+ for ( long t = 0 ; t < 1000 ; t ++ )
59+ {
60+ if ( iterator == linkedList . Last )
61+ {
62+ iterator = linkedList . First ;
63+ continue ;
64+ }
65+ iterator = iterator . Next ;
66+ }
67+
68+ sum += iterator . Value ;
69+ Console . WriteLine ( iterator . Value ) ;
70+ }
71+ Console . WriteLine ( sum ) ;
72+
73+ }
74+
75+ private static void Mix ( long index , LinkedList < long > linkedList , Dictionary < long , LinkedListNode < long > > nodes )
76+ {
77+ var originalNode = nodes [ index ] ;
78+
79+ var numberToMix = originalNode . Value ;
80+ if ( numberToMix > 0 )
81+ {
82+ var iteratorNode = GetNextNode ( linkedList , originalNode ) ;
83+ linkedList . Remove ( originalNode ) ;
84+ var targetNode = GetNextNodeSlow ( linkedList , numberToMix - 1 , iteratorNode ) ;
85+ linkedList . AddAfter ( targetNode , originalNode ) ;
86+ }
87+
88+ if ( numberToMix < 0 )
89+ {
90+ var iteratorNode = GetPrevNode ( linkedList , originalNode ) ;
91+ //Console.WriteLine($"prev node is {iteratorNode.Value}");
92+ linkedList . Remove ( originalNode ) ;
93+ var targetNode = GetPrevNodeSlow ( linkedList , Math . Abs ( numberToMix ) - 1 , iteratorNode ) ;
94+ linkedList . AddBefore ( targetNode , originalNode ) ;
95+ }
96+ }
97+
98+ private static LinkedListNode < long > GetNextNodeSlow ( LinkedList < long > linkedList , long numberToMix , LinkedListNode < long > iteratorNode )
99+ {
100+ numberToMix %= linkedList . Count ;
101+ for ( long i = 0 ; i < numberToMix ; i ++ )
102+ {
103+ iteratorNode = GetNextNode ( linkedList , iteratorNode ) ;
104+ }
105+ return iteratorNode ;
106+ }
107+
108+ private static LinkedListNode < long > GetPrevNodeSlow ( LinkedList < long > linkedList , long numberToMix , LinkedListNode < long > iteratorNode )
109+ {
110+ numberToMix %= linkedList . Count ;
111+ for ( long i = 0 ; i < numberToMix ; i ++ )
112+ {
113+ iteratorNode = GetPrevNode ( linkedList , iteratorNode ) ;
114+ //Console.WriteLine($"iterator node is now {iteratorNode.Value}");
115+ }
116+ return iteratorNode ;
117+ }
118+
119+ private static LinkedListNode < long > GetNextNode ( LinkedList < long > linkedList , LinkedListNode < long > nodeIterator )
120+ {
121+ if ( nodeIterator == linkedList . Last )
122+ {
123+ return linkedList . First ;
124+ }
125+ return nodeIterator . Next ;
126+ }
127+
128+ private static LinkedListNode < long > GetPrevNode ( LinkedList < long > linkedList , LinkedListNode < long > nodeIterator )
129+ {
130+ if ( nodeIterator == linkedList . First )
131+ {
132+ return linkedList . Last ;
133+ }
134+ return nodeIterator . Previous ;
135+ }
136+ }
137+
138+ internal static class IndexOfExtension {
139+
140+ public static long IndexOf < T > ( this LinkedList < T > linkedList , LinkedListNode < T > node )
141+ {
142+ var index = 0 ;
143+ var iterator = linkedList . First ;
144+
145+ while ( iterator != node )
146+ {
147+ index ++ ;
148+ iterator = iterator . Next ;
149+ }
150+
151+ return index ;
152+ }
153+
154+ public static LinkedListNode < T > NodeAt < T > ( this LinkedList < T > linkedList , long index )
155+ {
156+ var iterator = linkedList . First ;
157+
158+ for ( long i = 0 ; i < index ; i ++ )
159+ {
160+ iterator = iterator . Next ;
161+ }
162+
163+ return iterator ;
164+ }
165+
166+ }
167+ }
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