advent-of-code-2023/day4/solution.go

135 lines
2.3 KiB
Go

package main
import (
"errors"
"fmt"
"os"
"strconv"
"strings"
)
func noErr(err error) {
if err != nil {
panic(err)
}
}
func main() {
// parsing
input, err := os.ReadFile("input.txt")
noErr(err)
lines := strings.Split(string(input), "\n")
cards := make([]Card, len(lines))
cardCounts := map[int]int{}
for idx, l := range lines {
card, err := LineToCard(l)
noErr(err)
cards[idx] = card
cardCounts[card.Id] = 1
}
// part 1
s := 0
for _, c := range cards {
s += c.Points()
}
println("Part 1:", s)
// part 2
t := 0
for _, c := range cards {
t += cardCounts[c.Id]
for n := 1; n <= c.Wins(); n++ {
_, exists := cardCounts[c.Id+n]
if exists {
cardCounts[c.Id+n] += cardCounts[c.Id]
}
}
}
println("Part 2:", t)
}
type Card struct {
Id int
WinningNs []int
MyNs []int
}
func (card Card) Wins() int {
c := 0
for _, w := range card.WinningNs {
for _, n := range card.MyNs {
if w == n {
c++
}
}
}
return c
}
func (card Card) Points() int {
// math.Pow with into to float conversion feels wrong
p := 1
for _, w := range card.WinningNs {
for _, n := range card.MyNs {
if w == n {
p *= 2
}
}
}
if p == 1 {
return 0
}
return p / 2
}
var NoCutErr = errors.New("no cut found")
func LineToCard(line string) (Card, error) {
cardIdStr, nStr, f := strings.Cut(line, ":")
if !f {
return Card{}, fmt.Errorf("cut ':': %w", NoCutErr)
}
_, idStr, f := strings.Cut(cardIdStr, " ")
if !f {
return Card{}, fmt.Errorf("cut ' ': %w", NoCutErr)
}
id, err := strconv.Atoi(strings.TrimSpace(idStr))
if err != nil {
return Card{}, fmt.Errorf("card id: %w", err)
}
cardNStrs, myNStrs, f := strings.Cut(nStr, "|")
if !f {
return Card{}, fmt.Errorf("cut '|': %w", NoCutErr)
}
cardNs, err := strToNumbers(cardNStrs)
if err != nil {
return Card{}, fmt.Errorf("card ns: %w", err)
}
myNs, err := strToNumbers(myNStrs)
if err != nil {
return Card{}, fmt.Errorf("my ns: %w", err)
}
return Card{
Id: id,
WinningNs: cardNs,
MyNs: myNs,
}, nil
}
func strToNumbers(str string) ([]int, error) {
nStrs := strings.Split(str, " ")
ns := make([]int, 0)
for _, nStr := range nStrs {
if nStr == "" {
continue
}
n, err := strconv.Atoi(strings.TrimSpace(nStr))
if err != nil {
return nil, err
}
ns = append(ns, n)
}
return ns, nil
}