day 06 - sadly naive solution works

2023/day06/main.go

@@ -0,0 +1,141 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	races := parseInputPart1(input)
+	ans := 1
+
+	for _, r := range races {
+		ans *= wayToWinRace(r)
+	}
+
+	return ans
+}
+
+func wayToWinRace(r race) int {
+	// probably fast enough to do this naively for part 1...
+	// Time:        40     92     97     90
+	// total: 319
+	// but could binary search this
+
+	var ans int
+	for chargeTime := 1; chargeTime < r.time; chargeTime++ {
+		// velocity (chargeTime) * remaining time
+		dist := chargeTime * (r.time - chargeTime)
+		if dist > r.distance {
+			ans++
+		}
+	}
+
+	return ans
+}
+
+func part2(input string) int {
+	combinedRace := parseInputPart2(input)
+
+	// binary search this?
+	// but the left and right and middle could all fail if the distribution is
+	// F F P P P P F F F F F F F F F F F F
+	// F = Fail, P = Pass
+	// and it is some kind of (UN-CENTERED) bell curve distribution
+	// could test 1 by 1 from left and right of time bound...
+
+	// unfortunately you can just brute force this.
+	return wayToWinRace(combinedRace)
+
+	// all the optimizations might fall apart given unkind inputs, the example
+	// has a distribution with many passes in the middle:
+	// F P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P F
+	// but an unkind one could have F P F F F F F F F F F F F F F F F which could
+	// create a linear time complexity anyways...
+
+	// maybe there's some kind of search where you divide the input times until
+	// you find a passing time, so in half, then quarters, then eights, etc
+	// once you find a passing time you have a reduced window to search
+	// but if the entire entry is 0 or 1 pass and the rest fails, then it
+	// degrades to linear in the worst case scenario anyways, so sanitized or
+	// expected inputs do go a long way
+}
+
+type race struct {
+	time, distance int
+}
+
+func parseInputPart1(input string) (ans []race) {
+	parts := strings.Split(input, "\n")
+	timeParts := strings.Split(parts[0], " ")
+	distParts := strings.Split(parts[1], " ")
+
+	numRegexp := regexp.MustCompile("[0-9]+")
+
+	var t, d int
+	for t < len(timeParts) && d < len(distParts) {
+		for !numRegexp.MatchString(timeParts[t]) {
+			t++
+		}
+		for !numRegexp.MatchString(distParts[d]) {
+			d++
+		}
+		ans = append(ans, race{
+			time:     cast.ToInt(timeParts[t]),
+			distance: cast.ToInt(distParts[d]),
+		})
+		t++
+		d++
+	}
+
+	return ans
+}
+
+func parseInputPart2(input string) race {
+	parts := strings.Split(input, "\n")
+	timeLine := parts[0]
+	distLine := parts[1]
+
+	nonNums := regexp.MustCompile("[^0-9]+")
+	timeLine = nonNums.ReplaceAllString(timeLine, "")
+	distLine = nonNums.ReplaceAllString(distLine, "")
+
+	return race{
+		time:     cast.ToInt(timeLine),
+		distance: cast.ToInt(distLine),
+	}
+}