solve day 6 (with maths)

2023/day05_almanac.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"io"
 	"slices"
-	"strconv"
 	"strings"
 )
 
@@ -105,19 +104,6 @@ type day05SeedRange struct {
 	start, end int
 }
 
-func lineToInts(line string) []int {
-	values := strings.Split(line, " ")
-	ints := make([]int, len(values))
-	for i, value := range values {
-		number, err := strconv.Atoi(value)
-		if err != nil {
-			panic(err)
-		}
-		ints[i] = number
-	}
-	return ints
-}
-
 type day05Range struct {
 	destStart, sourceStart, length int
 }

2023/day06_boats.go

@@ -0,0 +1,63 @@
+package _023
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"math"
+	"strings"
+)
+
+func Day06Part1(input io.Reader) (int, error) {
+	scanner := bufio.NewScanner(input)
+
+	scanner.Scan()
+	times := lineToInts(strings.TrimPrefix(scanner.Text(), "Time:"))
+	scanner.Scan()
+	distances := lineToInts(strings.TrimPrefix(scanner.Text(), "Distance:"))
+	fmt.Println(times, distances)
+
+	margin := 1
+
+	for i := 0; i < len(times); i++ {
+		x1, x2 := zeros(times[i], distances[i])
+		if distance(x1, times[i]) <= distances[i] {
+			x1++
+		}
+		margin *= x2 - x1
+	}
+
+	return margin, nil
+}
+
+func zeros(time, distance int) (int, int) {
+	t, d := float64(time), float64(distance)
+	delta := math.Sqrt(math.Pow(t, 2) - 4*d)
+	return int(math.Ceil((t - delta) / 2)), int(math.Ceil((t + delta) / 2))
+}
+
+func distance(timePress, timeMax int) int {
+	return timePress * (timeMax - timePress)
+}
+
+func Day06Part2(input io.Reader) (int, error) {
+	scanner := bufio.NewScanner(input)
+
+	scanner.Scan()
+	times := lineToInts(strings.ReplaceAll(strings.TrimPrefix(scanner.Text(), "Time:"), " ", ""))
+	scanner.Scan()
+	distances := lineToInts(strings.ReplaceAll(strings.TrimPrefix(scanner.Text(), "Distance:"), " ", ""))
+	fmt.Println(times, distances)
+
+	margin := 1
+
+	for i := 0; i < len(times); i++ {
+		x1, x2 := zeros(times[i], distances[i])
+		if distance(x1, times[i]) <= distances[i] {
+			x1++
+		}
+		margin *= x2 - x1
+	}
+
+	return margin, nil
+}

2023/day06_boats_test.go

@@ -0,0 +1,25 @@
+package _023
+
+import (
+	"testing"
+)
+
+func TestDay06Part1(t *testing.T) {
+	tests := []testCase{
+		{"inputs/day06_test1", 288},
+		{"inputs/day06", 1660968},
+	}
+	for _, test := range tests {
+		t.Run(test.filename, check(test, Day06Part1))
+	}
+}
+
+func TestDay06Part2(t *testing.T) {
+	tests := []testCase{
+		{"inputs/day06_test1", 71503},
+		{"inputs/day06", 26499773},
+	}
+	for _, test := range tests {
+		t.Run(test.filename, check(test, Day06Part2))
+	}
+}

2023/inputs/day06

@@ -0,0 +1,2 @@
+Time:        47     98     66     98
+Distance:   400   1213   1011   1540

2023/inputs/day06_test1

@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200

2023/lib.go

@@ -0,0 +1,23 @@
+package _023
+
+import (
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var reg = regexp.MustCompile(`\s+`)
+
+func lineToInts(line string) []int {
+	line = strings.TrimSpace(line)
+	values := reg.Split(line, -1)
+	ints := make([]int, len(values))
+	for i, value := range values {
+		number, err := strconv.Atoi(value)
+		if err != nil {
+			panic(err)
+		}
+		ints[i] = number
+	}
+	return ints
+}