day6, part2

day6/daySix.go

@@ -0,0 +1,105 @@
+package day6
+
+import (
+	"fmt"
+	"log"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func Run() int {
+	race := ReadInput2("day6/input")
+
+	log.Printf("input %+v\n", race)
+	return race.countWinningMoves()
+}
+
+type Race struct {
+	Time, Target int
+}
+
+func (r Race) countWinningMoves() int {
+	// oh and it's simmetrical
+	leftPad := 0
+	rightPad := 0
+	for i := 0; i < (r.Time / 2 + 1); i++ {
+		if i * (r.Time - i) > r.Target {
+			leftPad = i
+			break
+		}
+	}
+	for i := 0; i < (r.Time / 2 + 1); i++ {
+		time := r.Time - i
+		if time * (r.Time - time) > r.Target {
+			rightPad = i
+			break
+		}
+	}
+
+	result := r.Time + 1 - leftPad - rightPad
+	log.Printf("for race %+v got left %d and right %d for total wind %d\n", r, leftPad, rightPad, result)
+	return result
+}
+
+func ReadInput2(filename string) Race {
+	runningTime := 0
+	runningDistance := 0
+
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(fmt.Sprintln("problem readin input : ", filename))
+	}
+	text := strings.Split( string(bytes), "\n")
+	times := strings.Fields(text[0])
+	distances := strings.Fields(text[1])
+
+	for i := 1; i < len(times); i++ {
+		timeStr := times[i]
+		distanceStr := distances[i]
+		time, err1 := strconv.Atoi(timeStr)
+		distance, err2 := strconv.Atoi(distanceStr)
+		if err1 != nil || err2 != nil {
+			panic(fmt.Sprintf("error reading race %d from %s %s\n", i, times[i], distances[i]))
+		}
+
+		runningTime = runningTime * int(math.Pow10(len(timeStr))) + time
+		runningDistance = runningDistance * int(math.Pow10(len(distanceStr))) + distance
+	}
+
+	return Race{ runningTime, runningDistance }
+}
+
+func ReadInput(filename string) []Race {
+	result := make([]Race, 0)
+
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		panic(fmt.Sprintln("problem readin input : ", filename))
+	}
+	text := strings.Split( string(bytes), "\n")
+	times := strings.Fields(text[0])
+	distances := strings.Fields(text[1])
+
+	for i := 1; i < len(times); i++ {
+		time, err1 := strconv.Atoi(times[i])
+		target, err2 := strconv.Atoi(distances[i])
+		if err1 != nil || err2 != nil {
+			panic(fmt.Sprintf("error reading race %d from %s %s\n", i, times[i], distances[i]))
+		}
+		race := Race{
+			Time: time,
+			Target: target,
+		}
+		result = append(result, race)
+	}
+
+	return result
+}
+
+
+
+// my guess is that i can search from start and end into middle and stop when i find solution
+// from the way i think derivation of x*y works
+// but first - read in the input. with strings.Fields should be easy

day6/example

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

day6/input

@@ -0,0 +1,2 @@
+Time:        40     82     91     66
+Distance:   277   1338   1349   1063

main.go

@@ -3,11 +3,11 @@ package main
 import (
 	"log"
 
-	"sunshine.industries/aoc2023/day5"
+	"sunshine.industries/aoc2023/day6"
 )
 
 func main() {
 	log.Print("> starting run:")
-	result := day5.Run()
+	result := day6.Run()
 	log.Printf("day4 result: %d\n****\n", result)
 }