day 4

go.mod

@@ -1,3 +1,7 @@
 module git.bizdoc.ro/gabi-public/Advent-of-Code.git
 
 go 1.25.1
+
+require git.bizdoc.ro/private/devkit.git v0.0.0-20250902190935-21cc248cb135
+
+require golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f // indirect

go.sum

@@ -0,0 +1,4 @@
+git.bizdoc.ro/private/devkit.git v0.0.0-20250902190935-21cc248cb135 h1:mUorxNlLlyvmPuZMKP80RFJVRcI1j85u1g8TDPht7AM=
+git.bizdoc.ro/private/devkit.git v0.0.0-20250902190935-21cc248cb135/go.mod h1:r/tE3YYNlrYNQc9DF4ph2Ur5WYKCtaqOM+8jqvzSoAQ=
+golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f h1:XdNn9LlyWAhLVp6P/i8QYBW+hlyhrhei9uErw2B5GJo=
+golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f/go.mod h1:D5SMRVC3C2/4+F/DB1wZsLRnSNimn2Sp/NPsCrsv8ak=

year25/day1.go

@@ -5,11 +5,10 @@ import (
 	"fmt"
 	"io"
 	"iter"
-	"log"
 	"strconv"
 )
 
-func Day1Part1(r io.Reader, l *log.Logger) (any, error) {
+func Day1Part1(r io.Reader, l Logger) (any, error) {
 	dial := 50
 	solution := 0
 	for pair := range day1GetPairs(r) {
@@ -27,7 +26,7 @@ func Day1Part1(r io.Reader, l *log.Logger) (any, error) {
 	return solution, nil
 }
 
-func Day1Part2Slow(r io.Reader, l *log.Logger) (any, error) {
+func Day1Part2Slow(r io.Reader, l Logger) (any, error) {
 	dial := 50
 	solution := 0
 	for pair := range day1GetPairs(r) {
@@ -45,7 +44,7 @@ func Day1Part2Slow(r io.Reader, l *log.Logger) (any, error) {
 	return solution, nil
 }
 
-func Day1Part2Fast(r io.Reader, l *log.Logger) (any, error) {
+func Day1Part2Fast(r io.Reader, l Logger) (any, error) {
 	dial := 50
 	solution := 0
 	for pair := range day1GetPairs(r) {

year25/day2.go

@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"log"
 	"strconv"
 	"strings"
 
@@ -51,7 +50,7 @@ func (s *day2Scanner) Bounds() (int, int) {
 	return s.a, s.b
 }
 
-func Day2Part1Simple(r io.Reader, l *log.Logger) (any, error) {
+func Day2Part1Simple(r io.Reader, l Logger) (any, error) {
 	input, err := aocutils.ReadString(r)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read input: %s", err)
@@ -95,7 +94,7 @@ func Day2Part1Simple(r io.Reader, l *log.Logger) (any, error) {
 	return sum, nil
 }
 
-func Day2Part2Simple(r io.Reader, l *log.Logger) (any, error) {
+func Day2Part2Simple(r io.Reader, l Logger) (any, error) {
 	input, err := aocutils.ReadString(r)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read input: %s", err)
@@ -155,7 +154,7 @@ func Day2Part2Simple(r io.Reader, l *log.Logger) (any, error) {
 	return sum, nil
 }
 
-func Day2Part1(r io.Reader, logger *log.Logger) (any, error) {
+func Day2Part1(r io.Reader, logger Logger) (any, error) {
 	inputScanner := bufio.NewScanner(r)
 	inputScanner.Split(aocutils.SplitComma)
 	scanner := &day2Scanner{scanner: inputScanner, sep: '-'}
@@ -182,7 +181,7 @@ func Day2Part1(r io.Reader, logger *log.Logger) (any, error) {
 	return sum, scanner.Err()
 }
 
-func Day2Part2(r io.Reader, logger *log.Logger) (any, error) {
+func Day2Part2(r io.Reader, logger Logger) (any, error) {
 	inputScanner := bufio.NewScanner(r)
 	inputScanner.Split(aocutils.SplitComma)
 

year25/day3.go

@@ -4,17 +4,16 @@ import (
 	"bufio"
 	"fmt"
 	"io"
-	"log"
 	"strings"
 )
 
-func Day3Part1(r io.Reader, l *log.Logger) (any, error) {
+func Day3Part1(r io.Reader, l Logger) (any, error) {
 	return Day3(r, l, 2)
 }
-func Day3Part2(r io.Reader, l *log.Logger) (any, error) {
+func Day3Part2(r io.Reader, l Logger) (any, error) {
 	return Day3(r, l, 12)
 }
-func Day3(r io.Reader, logger *log.Logger, size int) (int64, error) {
+func Day3(r io.Reader, logger Logger, size int) (int64, error) {
 	scanner := bufio.NewScanner(r)
 	scanner.Split(bufio.ScanLines)
 	var sum int64

year25/day4.go

@@ -0,0 +1,78 @@
+package year25
+
+import (
+	"fmt"
+	"io"
+
+	"git.bizdoc.ro/private/devkit.git/collections/geometry/v2"
+)
+
+const Day4PaperRoll = '@'
+
+func Day4Part1(r io.Reader, l Logger) (any, error) {
+	// 4 rolls in 8 adjacent positions
+
+	var accessibleRolls int
+	g, err := geometry.ReaderToByteGrid(r)
+	if err != nil {
+		return nil, fmt.Errorf("day4: failed to read grid: %w", err)
+	}
+
+	for c := range g.Points() {
+		if g.At(c) != Day4PaperRoll {
+			continue
+		}
+
+		var count int
+		for p := range g.SubgridPointsIter(c.MoveUpLeft(), c.MoveDownRight()) {
+			if g.At(p) == Day4PaperRoll {
+				count += 1
+			}
+		}
+
+		if count <= 4 {
+			accessibleRolls += 1
+		}
+	}
+
+	return accessibleRolls, nil
+}
+
+func Day4Part2(r io.Reader, l Logger) (any, error) {
+	// 4 rolls in 8 adjacent positions
+
+	var totalRemovedRolls int
+	g, err := geometry.ReaderToByteGrid(r)
+	if err != nil {
+		return nil, fmt.Errorf("day4: failed to read grid: %w", err)
+	}
+
+	for {
+		removedRolls := 0
+		for c := range g.Points() {
+			if g.At(c) != Day4PaperRoll {
+				continue
+			}
+
+			var count int
+			for p := range g.SubgridPointsIter(c.MoveUpLeft(), c.MoveDownRight()) {
+				if g.At(p) == Day4PaperRoll {
+					count += 1
+				}
+			}
+
+			if count <= 4 {
+				removedRolls += 1
+				g.Set(c, '.') // remove grid
+			}
+		}
+
+		if removedRolls == 0 {
+			break
+		}
+
+		totalRemovedRolls += removedRolls
+	}
+
+	return totalRemovedRolls, nil
+}

year25/utils.go

@@ -0,0 +1,6 @@
+package year25
+
+type Logger interface {
+	Printf(string, ...interface{})
+	Println(...interface{})
+}