2022 day 15

Author: pvainio

2022/go/day15/day15.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+func main() {
+	input, _ := os.ReadFile("../../input/day15.txt")
+	sensors := readInput(string(input))
+
+	spans, count := spansForY(sensors, 2000000), 0
+	for _, s := range spans {
+		count += s.end - s.start
+	}
+
+	fmt.Printf("part1: %v\n", count)
+
+	var x, y int
+	for y = 0; y <= 4000000; y++ {
+		spans := spansForY(sensors, y)
+		if len(spans) > 1 {
+			x = spans[0].end + 1
+			break
+		}
+	}
+	fmt.Printf("part2: %v\n", x*4000000+y)
+}
+
+func spansForY(sensors []sensor, y int) (spans []span) {
+	for _, s := range sensors {
+		sbDist, srDist := abs(s.loc.x-s.beacon.x)+abs(s.loc.y-s.beacon.y), abs(s.loc.y-y)
+		dist := sbDist - srDist
+		if dist > 0 {
+			spans = append(spans, span{s.loc.x - dist, s.loc.x + dist})
+		}
+	}
+	return merge(spans)
+}
+
+func merge(spans []span) (res []span) {
+	sort.Sort(byStart(spans))
+	res = append(res, spans[0])
+	for _, next := range spans[1:] {
+		prev := res[len(res)-1]
+		if prev.end >= next.start-1 {
+			res[len(res)-1] = span{prev.start, max(prev.end, next.end)}
+		} else {
+			res = append(res, next)
+		}
+	}
+	return res
+}
+
+func readInput(input string) (res []sensor) {
+	lines := strings.Split(input, "\n")
+	for _, l := range lines {
+		var s sensor
+		fmt.Sscanf(l, "Sensor at x=%d, y=%d: closest beacon is at x=%d, y=%d",
+			&s.loc.x, &s.loc.y, &s.beacon.x, &s.beacon.y)
+		res = append(res, s)
+	}
+	return res
+}
+
+type span struct{ start, end int }
+type sensor struct{ loc, beacon xy }
+type xy struct{ x, y int }
+type byStart []span
+
+func (a byStart) Len() int           { return len(a) }
+func (a byStart) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byStart) Less(i, j int) bool { return a[i].start < a[j].start }
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func abs(v int) int {
+	if v < 0 {
+		return -v
+	}
+	return v
+}

2022/input/day15.txt

@@ -0,0 +1,33 @@
+Sensor at x=1555825, y=18926: closest beacon is at x=1498426, y=-85030
+Sensor at x=697941, y=3552290: closest beacon is at x=595451, y=3788543
+Sensor at x=3997971, y=2461001: closest beacon is at x=3951198, y=2418718
+Sensor at x=3818312, y=282332: closest beacon is at x=4823751, y=1061753
+Sensor at x=2874142, y=3053631: closest beacon is at x=3074353, y=3516891
+Sensor at x=1704479, y=2132468: closest beacon is at x=1749091, y=2000000
+Sensor at x=3904910, y=2080560: closest beacon is at x=3951198, y=2418718
+Sensor at x=657061, y=3898803: closest beacon is at x=595451, y=3788543
+Sensor at x=3084398, y=3751092: closest beacon is at x=3074353, y=3516891
+Sensor at x=2582061, y=972407: closest beacon is at x=1749091, y=2000000
+Sensor at x=2886721, y=3971936: closest beacon is at x=3074353, y=3516891
+Sensor at x=303399, y=548513: closest beacon is at x=-1010425, y=986825
+Sensor at x=3426950, y=2290126: closest beacon is at x=3951198, y=2418718
+Sensor at x=3132858, y=3592272: closest beacon is at x=3074353, y=3516891
+Sensor at x=3773724, y=3751243: closest beacon is at x=3568452, y=3274758
+Sensor at x=3987212, y=2416515: closest beacon is at x=3951198, y=2418718
+Sensor at x=61559, y=3806326: closest beacon is at x=595451, y=3788543
+Sensor at x=2693503, y=2291389: closest beacon is at x=2269881, y=2661753
+Sensor at x=3953437, y=2669220: closest beacon is at x=3951198, y=2418718
+Sensor at x=763035, y=3997568: closest beacon is at x=595451, y=3788543
+Sensor at x=3999814, y=2370103: closest beacon is at x=3951198, y=2418718
+Sensor at x=1290383, y=1696257: closest beacon is at x=1749091, y=2000000
+Sensor at x=3505508, y=2805537: closest beacon is at x=3568452, y=3274758
+Sensor at x=3276207, y=3323122: closest beacon is at x=3568452, y=3274758
+Sensor at x=2244609, y=3517499: closest beacon is at x=3074353, y=3516891
+Sensor at x=1370860, y=3436382: closest beacon is at x=595451, y=3788543
+Sensor at x=3831063, y=3042662: closest beacon is at x=3568452, y=3274758
+Sensor at x=551202, y=3971545: closest beacon is at x=595451, y=3788543
+Sensor at x=336629, y=2519780: closest beacon is at x=595451, y=3788543
+Sensor at x=2033602, y=2882628: closest beacon is at x=2269881, y=2661753
+Sensor at x=3939808, y=2478271: closest beacon is at x=3951198, y=2418718
+Sensor at x=1958708, y=2370822: closest beacon is at x=1749091, y=2000000
+Sensor at x=3039958, y=3574483: closest beacon is at x=3074353, y=3516891

2022/java/Day15.java

@@ -0,0 +1,58 @@
+import java.nio.file.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.regex.Pattern;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+class Day15 {
+
+    public static void main(String ... args) throws Exception {
+        var lines = Files.readString(Path.of("../input/day15.txt")).split("\n");
+        var sensors = Arrays.stream(lines).map(Sensor::parse).toList();
+
+        var count = rangesForY(sensors, 2000000).stream().mapToLong(r -> r.end() - r.start()).sum();
+        System.out.printf("part1: %d\n", count);
+
+        var freq = IntStream.range(0, 4000000)
+            .mapToObj(y -> rangesForY(sensors, y))
+            .filter(rs -> rs.size() > 1) // find the one hole in the middle, two ranges
+            .map(rs -> rs.get(0)) // get the first range, location is after it end
+            .map(r -> (r.end + 1)*4000000+r.y) // calculate the frequency
+            .findFirst().get();
+    
+        System.out.printf("part2: %d\n", freq);
+    }
+
+    static List<Range> rangesForY(List<Sensor> sensors, int y) {
+        var ranges = sensors.stream().flatMap(s -> {
+            var beaconDist = Math.abs(s.loc.x - s.beacon.x) + Math.abs(s.loc.y - s.beacon.y);
+            var dist = beaconDist - Math.abs(s.loc.y - y); // x distance for this sensor for this y
+            return dist > 0 ? Stream.of(new Range(s.loc.x - dist, s.loc.x + dist, y)) : Stream.of();
+        }).sorted((a,b) -> (int) (a.start()-b.start())).toList(); // sorted ranges
+        // merge adjoining or overlapping ranges
+        LinkedList<Range> res = new LinkedList<>(List.of(ranges.get(0)));
+        for (var next : ranges.subList(1, ranges.size())) {
+            var prev = res.getLast();
+            if (prev.end() >= next.start() - 1) {
+                res.removeLast();
+                res.add(new Range(prev.start(), Math.max(prev.end(), next.end()), y));
+            } else {
+                res.add(next);
+            }
+        }
+        return res;
+    }
+    
+    record Range (long start, long end, long y) {}
+    record XY(long x, long y) {}
+    record Sensor(XY loc, XY beacon) {
+        static Sensor parse(String line) {
+            var m = Pattern.compile("=(-?\\d+)").matcher(line);
+            var ns = m.results().mapToInt(r -> Integer.parseInt(r.group(1))).toArray();
+            return new Sensor(new XY(ns[0], ns[1]), new XY(ns[2], ns[3]));
+        }
+    }
+ }