1+ package com .macasaet ;
2+
3+ import java .util .ArrayList ;
4+ import java .util .LinkedList ;
5+ import java .util .List ;
6+ import java .util .stream .Stream ;
7+ import java .util .stream .StreamSupport ;
8+
9+ import org .junit .jupiter .api .Test ;
10+
11+ /**
12+ * --- Day 10: Syntax Scoring ---
13+ */
14+ public class Day10 {
15+
16+ protected Stream <String > getInput () {
17+ return StreamSupport
18+ .stream (new LineSpliterator ("day-10.txt" ),
19+ false );
20+ }
21+
22+ /**
23+ * The type of open and closing delimiter for a chunk in the navigation subsystem
24+ */
25+ public enum BracketType {
26+ PARENTHESIS ('(' , ')' , 3 , 1 ),
27+ SQUARE ('[' , ']' , 57 , 2 ),
28+ CURLY ('{' , '}' , 1197 , 3 ),
29+ ANGLED ('<' , '>' , 25137 , 4 );
30+
31+ private final char open ;
32+ private final char close ;
33+ private final int corruptionPoints ;
34+ private final int autocompletePoints ;
35+
36+ BracketType (char open , char close , int corruptionPoints , final int autocompletePoints ) {
37+ this .open = open ;
38+ this .close = close ;
39+ this .corruptionPoints = corruptionPoints ;
40+ this .autocompletePoints = autocompletePoints ;
41+ }
42+
43+ public static BracketType forOpen (final char c ) {
44+ return switch (c ) {
45+ case '(' -> PARENTHESIS ;
46+ case '[' -> SQUARE ;
47+ case '{' -> CURLY ;
48+ case '<' -> ANGLED ;
49+ default -> throw new IllegalStateException ("Unexpected value: " + c );
50+ };
51+ }
52+
53+ public static BracketType forClose (final char c ) {
54+ return switch (c ) {
55+ case ')' -> PARENTHESIS ;
56+ case ']' -> SQUARE ;
57+ case '}' -> CURLY ;
58+ case '>' -> ANGLED ;
59+ default -> throw new IllegalStateException ("Unexpected value: " + c );
60+ };
61+ }
62+ }
63+
64+ /**
65+ * @param line a line in the navigation subsystem
66+ * @return a score of how corrupt the line is. A score of zero means it is not corrupt. The higher the value, the
67+ * more corrupt the line is.
68+ */
69+ public int calculateCorruptionScore (final char [] line ) {
70+ final var stack = new LinkedList <BracketType >();
71+ for (int i = 0 ; i < line .length ; i ++) {
72+ final var c = line [i ];
73+ if (c == '(' || c == '[' || c == '{' || c == '<' ) {
74+ stack .push (BracketType .forOpen (c ));
75+ } else if (c == ')' || c == ']' || c == '}' || c == '>' ) {
76+ if (stack .peek ().close == c ) {
77+ stack .pop ();
78+ } else {
79+ // corrupt
80+ return BracketType .forClose (c ).corruptionPoints ;
81+ }
82+ }
83+ }
84+ // if stack is not empty, it's incomplete
85+ return 0 ;
86+ }
87+
88+ /**
89+ * @param line a non-corrupt line in the navigation subsystem. Behaviour is undefined for corrupt lines.
90+ * @return the score for the suffix required to complete the line
91+ */
92+ public long calculateCompletionScore (final char [] line ) {
93+ final var stack = new LinkedList <BracketType >();
94+ for (int i = 0 ; i < line .length ; i ++) {
95+ final var c = line [i ];
96+ if (c == '(' || c == '[' || c == '{' || c == '<' ) {
97+ stack .push (BracketType .forOpen (c ));
98+ } else if (c == ')' || c == ']' || c == '}' || c == '>' ) {
99+ if (stack .peek ().close == c ) {
100+ stack .pop ();
101+ } else {
102+ throw new IllegalArgumentException ("Corrupt: " + new String (line ));
103+ }
104+ }
105+ }
106+ long result = 0 ;
107+ while (!stack .isEmpty ()) {
108+ final var unclosed = stack .pop ();
109+ result = result * 5 + unclosed .autocompletePoints ;
110+ }
111+ return result ;
112+ }
113+
114+ @ Test
115+ public final void part1 () {
116+ final var result = getInput ()
117+ .map (String ::toCharArray )
118+ .filter (line -> line .length > 0 )
119+ .mapToInt (this ::calculateCorruptionScore )
120+ .sum ();
121+ System .out .println ("Part 1: " + result );
122+ }
123+
124+ @ Test
125+ public final void part2 () {
126+ final var list = getInput ()
127+ .map (String ::toCharArray )
128+ .filter (line -> line .length > 0 )
129+ .filter (line -> calculateCorruptionScore (line ) <= 0 ) // discard corrupted lines
130+ .mapToLong (this ::calculateCompletionScore )
131+ .sorted ()
132+ .collect (ArrayList <Long >::new , List ::add , List ::addAll );
133+ final var result = list .get (list .size () / 2 );
134+ System .out .println ("Part 2: " + result );
135+ }
136+
137+ }
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