parallelize day 21 part 2, for funsies

codeforkjeff · codeforkjeff · commit f77677fe3c22 · 2025-01-11T21:43:44.000-08:00
diff --git a/src/main/java/com/codefork/aoc2024/day21/Part02.java b/src/main/java/com/codefork/aoc2024/day21/Part02.java
@@ -7,7 +7,7 @@
 public class Part02 extends Problem {
 
     public String solve(Stream<String> data) {
-        System.out.println("TODO: This takes ~1.5 minutes to run, needs to be optimized");
+        System.out.println("TODO: This takes ~1 minute to run, needs to be optimized");
         return String.valueOf(ShipLock.calculateSumOfComplexities(data, 25));
     }
 
diff --git a/src/main/java/com/codefork/aoc2024/day21/ShipLock.java b/src/main/java/com/codefork/aoc2024/day21/ShipLock.java
@@ -43,9 +43,13 @@ record WithLength(PressSequence seq, long length) {
                     for (var navigator : navigators) {
                         var newPressSeqSet = new HashSet<PressSequence>();
                         // one to many results
-                        for (var pressSeq : pressSeqs) {
-                            var possiblePresses = navigator.getPossiblePressSequences(pressSeq);
-                            newPressSeqSet.addAll(possiblePresses);
+
+                        // parallelization on my laptop w/ 16 virtual cores cuts runtime by 1/3, from 83s to 57s
+                        var results = pressSeqs.parallelStream()
+                                .map(navigator::getPossiblePressSequences)
+                                .toList();
+                        for(var result : results) {
+                            newPressSeqSet.addAll(result);
                         }
 
                         // calculate lengths just once, since it's a slightly expensive operation

Original file line number	Diff line number	Diff line change
`@@ -7,7 +7,7 @@`
`7`	`7`	`public class Part02 extends Problem {`
`8`	`8`
`9`	`9`	`public String solve(Stream<String> data) {`
`10`		`- System.out.println("TODO: This takes ~1.5 minutes to run, needs to be optimized");`
	`10`	`+ System.out.println("TODO: This takes ~1 minute to run, needs to be optimized");`
`11`	`11`	`return String.valueOf(ShipLock.calculateSumOfComplexities(data, 25));`
`12`	`12`	`}`
`13`	`13`