1+ package com .macasaet ;
2+
3+ import java .io .IOException ;
4+ import java .math .BigInteger ;
5+ import java .util .ArrayList ;
6+
7+ public class Day23 {
8+
9+ public static void main (final String [] args ) throws IOException {
10+ final var labels = new ArrayList <Integer >();
11+ try (var inputStream = Day23 .class .getResourceAsStream ("/day-23-input.txt" )) {
12+ for (final var c : new String (inputStream .readAllBytes ()).strip ().toCharArray ()) {
13+ labels .add (Integer .parseInt ("" + c ));
14+ }
15+ }
16+
17+ final var map = new Cup [1_000_0000 + 1 ];
18+ Cup first = null ;
19+ Cup current = null ;
20+ int min = Integer .MAX_VALUE ;
21+ int max = Integer .MIN_VALUE ;
22+ for (final int label : labels ) {
23+ final var cup = new Cup (label );
24+ map [label ] = cup ;
25+ if (first == null ) {
26+ first = cup ;
27+ } else {
28+ current .next = cup ;
29+ }
30+ current = cup ;
31+
32+ min = Math .min (min , label );
33+ max = Math .max (max , label );
34+ }
35+
36+ for (int i = max + 1 ; i <= 1_000_000 ; i ++) { // Part 2
37+ final var cup = new Cup (i );
38+ map [i ] = cup ;
39+ current .next = cup ;
40+ current = cup ;
41+ }
42+ max = 1_000_000 ;
43+ current .next = first ;
44+ current = current .next ;
45+
46+ for (int moveId = 1 ; moveId <= 10_000_000 ; moveId ++) { // Part 1 looped only 100 times
47+ final var a = current .take ();
48+ final var b = current .take ();
49+ final var c = current .take ();
50+
51+ int destinationValue = current .label - 1 ;
52+ while (destinationValue == a .label || destinationValue == b .label || destinationValue == c .label || destinationValue < min || destinationValue > max ) {
53+ destinationValue --;
54+ if (destinationValue < min ) {
55+ destinationValue = max ;
56+ }
57+ }
58+
59+ final var destination = map [destinationValue ];
60+ c .linkBefore (destination .next );
61+ b .linkBefore (c );
62+ a .linkBefore (b );
63+ destination .linkBefore (a );
64+
65+ current = current .next ;
66+ }
67+ final var reference = map [1 ];
68+ // String result = "";
69+ // var cursor = reference.next;
70+ // for (int i = labels.size() - 1; --i >= 0; ) {
71+ // result += cursor.label;
72+ // cursor = cursor.next;
73+ // }
74+ // System.out.println("Part 1: " + result);
75+ final BigInteger x = new BigInteger ("" + map [reference .next .label ].label );
76+ final BigInteger y = new BigInteger ("" + map [reference .next .next .label ].label );
77+ System .out .println ("Part 2: " + x .multiply (y ).toString ());
78+ }
79+
80+ protected static class Cup {
81+ private final int label ;
82+ private Cup next ;
83+
84+ public Cup (final int label ) {
85+ this .label = label ;
86+ }
87+
88+ public Cup take () {
89+ final Cup retval = next ;
90+ next = retval .next ;
91+ retval .next = null ;
92+ return retval ;
93+ }
94+
95+ public void linkBefore (final Cup cup ) {
96+ next = cup ;
97+ }
98+
99+ public String toString () {
100+ return "Cup{ label=" + label + ", next=" + (next != null ? next .label : null ) + " }" ;
101+ }
102+ }
103+
104+ }
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