AoC 2020 Day 23 - java - faster

pareronia · pareronia · commit 9fc1a0c10ad2 · 2025-01-08T22:01:24.000+01:00
diff --git a/src/main/java/AoC2020_23.java b/src/main/java/AoC2020_23.java
@@ -1,20 +1,20 @@
+import static com.github.pareronia.aoc.IntegerSequence.Range.range;
+import static java.util.stream.Collectors.joining;
 import static java.util.stream.Collectors.toCollection;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.IntSummaryStatistics;
 import java.util.List;
-import java.util.Map;
-import java.util.Objects;
+import java.util.Set;
+import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
 import com.github.pareronia.aoc.StringOps;
 import com.github.pareronia.aoc.solution.Sample;
 import com.github.pareronia.aoc.solution.Samples;
 import com.github.pareronia.aoc.solution.SolutionBase;
 
-public class AoC2020_23 extends SolutionBase<List<Integer>, Long, Long> {
+public class AoC2020_23 extends SolutionBase<List<Integer>, String, Long> {
 	
 	private AoC2020_23(final boolean debug) {
 		super(debug);
@@ -35,92 +35,67 @@ protected List<Integer> parseInput(final List<String> inputs) {
         return Arrays.stream(digits).toList();
     }
 
-    private Map<Integer, Cup> prepareCups(final List<Integer> labels) {
-		final Map<Integer, Cup> cups = new HashMap<>();
-		final Integer first = labels.get(0);
-		final Integer last = labels.get(labels.size() - 1);
-		final Cup tail = new Cup(last, (Cup) null);
-		Cup prev = tail;
-		Cup cup;
-		for (int i = labels.size() - 2; i > 0; i--) {
-			final Integer label = labels.get(i);
-			cup = new Cup(label, prev);
-			cups.put(label, cup);
-			prev = cup;
-		}
-		final Cup head = new Cup(first, prev);
-		cups.put(first, head);
-		tail.setNext(head);
-		cups.put(last, tail);
-		return cups;
-	}
-	
-    private Cup doMove(
-            final Map<Integer, Cup> cups,
-            final Cup current,
-            final Integer size,
-            final Integer min,
-            final Integer max) {
-		final Cup p1 = current.getNext();
-		final Cup p2 = p1.getNext();
-		final Cup p3 = p2.getNext();
-		current.setNext(p3.getNext());
-		final List<Integer> pickup
-		        = List.of(p1.getLabel(), p2.getLabel(), p3.getLabel());
-		Integer d = current.getLabel() - 1;
-		if (d < min) {
-			d = max;
-		}
+    private int[] prepareCups(final List<Integer> labels) {
+        final int[] cups = new int[labels.size() + 1];
+        range(labels.size()).forEach(i -> {
+            cups[labels.get(i)] = labels.get((i + 1) % labels.size());
+        });
+        return cups;
+    }
+
+    private int doMove(
+            final int[] cups,
+            final int current,
+            final int min,
+            final int max
+    ) {
+        final int c = current;
+        final int p1 = cups[c];
+        final int p2 = cups[p1];
+        final int p3 = cups[p2];
+        cups[c] = cups[p3];
+        final Set<Integer> pickup = Set.of(p1, p2, p3);
+        int d = c - 1;
+        if (d < min) {
+            d = max;
+        }
 		while (pickup.contains(d)) {
 			d--;
 			if (d < min) {
 				d = max;
 			}
 		}
-		final Cup destination = cups.get(d);
-		p3.setNext(destination.getNext());
-		destination.setNext(p1);
-		return current.getNext();
-	}
-	
+		cups[p3] = cups[d];
+		cups[d] = p1;
+		return cups[c];
+    }
+
 	@Override
-	public Long solvePart1(final List<Integer> labels) {
-		final Map<Integer, Cup> cups = prepareCups(labels);
-		final int size = labels.size();
-		final IntSummaryStatistics stats
-		    = labels.stream().mapToInt(Integer::valueOf).summaryStatistics();
-		final Integer min = stats.getMin();
-		final Integer max = stats.getMax();
-		Cup current = cups.get(labels.get(0));
+	public String solvePart1(final List<Integer> labels) {
+	    final int[] cups = prepareCups(labels);
+		int current = labels.get(0);
 		for (int i = 0; i < 100; i++) {
-			current = doMove(cups, current, size, min, max);
+			current = doMove(cups, current, 1, 9);
 		}
-		Cup cup = cups.get(1);
-		final StringBuilder result = new StringBuilder();
-		while (cup.getNext().getLabel() != 1) {
-			result.append(cup.getNext().getLabel());
-			cup = cup.getNext();
-		}
-		return Long.valueOf(result.toString());
+		return IntStream.iterate(cups[1], cup -> cups[cup])
+		        .takeWhile(cup -> cup != 1)
+		        .mapToObj(String::valueOf)
+		        .collect(joining());
 	}
 	
 	@Override
 	public Long solvePart2(final List<Integer> labels) {
-		final IntSummaryStatistics stats
-		    = labels.stream().mapToInt(Integer::valueOf).summaryStatistics();
-		final Integer min = stats.getMin();
-		final Integer max = stats.getMax();
-		final List<Integer> newLabels = new ArrayList<>(labels);
-		Stream.iterate(max + 1, i -> i + 1).limit(1_000_000 - labels.size())
+		final List<Integer> newLabels = new ArrayList<>(1_000_000);
+		newLabels.addAll(labels);
+		Stream.iterate(10, i -> i + 1).limit(1_000_000 - labels.size())
 			.collect(toCollection(() -> newLabels));
-		final Map<Integer, Cup> cups = prepareCups(newLabels);
-		Cup current = cups.get(newLabels.get(0));
+		final int[] cups = prepareCups(newLabels);
+		int current = labels.get(0);
 		for (int i = 0; i < 10_000_000; i++) {
-			current = doMove(cups, current, 1_000_000, min, 1_000_000);
+			current = doMove(cups, current, 1, 1_000_000);
 		}
-		final Cup one = cups.get(1);
-		final long star1 = one.getNext().getLabel().longValue();
-		final long star2 = one.getNext().getNext().getLabel().longValue();
+		final long star1 = cups[1];
+		final long star2 = cups[cups[1]];
 		return star1 * star2;
 	}
 	
@@ -133,54 +108,4 @@ public static void main(final String[] args) throws Exception {
 	}
 	
 	private static final String TEST = "389125467";
-	
-	
-	private static final class Cup {
-		private final Integer label;
-		private Cup next;
-
-        public Cup(final Integer label, final Cup next) {
-            this.label = label;
-            this.next = next;
-        }
-
-        public Integer getLabel() {
-            return label;
-        }
-
-        public Cup getNext() {
-            return next;
-        }
-
-        public void setNext(final Cup next) {
-            this.next = next;
-        }
-        
-		@Override
-        public String toString() {
-            final StringBuilder builder = new StringBuilder();
-            builder.append("Cup [label=").append(label).append("]");
-            return builder.toString();
-        }
-
-        @Override
-        public boolean equals(final Object obj) {
-            if (this == obj) {
-                return true;
-            }
-            if (obj == null) {
-                return false;
-            }
-            if (getClass() != obj.getClass()) {
-                return false;
-            }
-            final Cup other = (Cup) obj;
-            return Objects.equals(label, other.label) && Objects.equals(next, other.next);
-        }
-
-        @Override
-        public int hashCode() {
-            return Objects.hash(label, next);
-        }
-	}
 }
diff --git a/src/main/java/com/github/pareronia/aoc/IterTools.java b/src/main/java/com/github/pareronia/aoc/IterTools.java
@@ -110,8 +110,8 @@ public static <T> IterToolsIterator<ZippedPair<T>> zip(
         return zip(iterable1.iterator(), iterable2.iterator());
     }
     
-    private static <T> Iterator<T> cycle(final Iterator<T> iterator) {
-        return new Iterator<>() {
+    private static <T> IterToolsIterator<T> cycle(final Iterator<T> iterator) {
+        return new IterToolsIterator<>() {
             List<T> saved = new ArrayList<>();
             int i = 0;
 
@@ -132,7 +132,7 @@ public T next() {
         };
     }
 
-    public static <T> Iterator<T> cycle(final Iterable<T> iterable) {
+    public static <T> IterToolsIterator<T> cycle(final Iterable<T> iterable) {
         return cycle(iterable.iterator());
     }
     

Original file line number	Diff line number	Diff line change
`@@ -110,8 +110,8 @@ public static <T> IterToolsIterator<ZippedPair<T>> zip(`
`110`	`110`	`return zip(iterable1.iterator(), iterable2.iterator());`
`111`	`111`	`}`
`112`	`112`
`113`		`- private static <T> Iterator<T> cycle(final Iterator<T> iterator) {`
`114`		`- return new Iterator<>() {`
	`113`	`+ private static <T> IterToolsIterator<T> cycle(final Iterator<T> iterator) {`
	`114`	`+ return new IterToolsIterator<>() {`
`115`	`115`	`List<T> saved = new ArrayList<>();`
`116`	`116`	`int i = 0;`
`117`	`117`
`@@ -132,7 +132,7 @@ public T next() {`
`132`	`132`	`};`
`133`	`133`	`}`
`134`	`134`
`135`		`- public static <T> Iterator<T> cycle(final Iterable<T> iterable) {`
	`135`	`+ public static <T> IterToolsIterator<T> cycle(final Iterable<T> iterable) {`
`136`	`136`	`return cycle(iterable.iterator());`
`137`	`137`	`}`
`138`	`138`