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|
package main
import (
"bufio"
"fmt"
"log"
"os"
"sort"
"strconv"
)
type (
t interface{}
empty struct{}
)
type packet struct {
data []t
}
func intOrList(v t) int {
switch v.(type) {
case int:
return 0
case []t:
return 1
default:
return -1
}
}
type compcode int
const (
cont compcode = -1
rightOrder compcode = 0
wrongOrder compcode = 1
)
// not very idiomatich i think
func newComparePackets(comp func(a, b int) compcode) func(p1, p2 *packet) (int, compcode) {
return func(p1, p2 *packet) (int, compcode) {
var cp func(i int, ok compcode, a, b []t) (int, compcode)
cp = func(i int, ok compcode, a, b []t) (int, compcode) {
if al, bl := i >= len(a), i >= len(b); al {
if bl && al {
return i, cont
}
if bl && !al {
return i, wrongOrder
}
return i, rightOrder
}
if al, bl := i >= len(a), i >= len(b); bl {
if bl && al {
return i, cont
}
if bl && !al {
return i, wrongOrder
}
return i, rightOrder
}
at, bt := intOrList(a[i]), intOrList(b[i])
code := cont
if at == 1 && bt == 1 {
_, code = cp(0, ok, a[i].([]t), b[i].([]t))
} else if at == 1 && bt == 0 {
_, code = cp(0, ok, a[i].([]t), []t{b[i]})
} else if at == 0 && bt == 1 {
_, code = cp(0, ok, []t{a[i]}, b[i].([]t))
} else if at == 0 && bt == 0 {
code = comp(a[i].(int), b[i].(int))
} else {
log.Fatal("Unexpected input types")
}
if code != cont {
return i, code
}
return cp((i + 1), code, a, b)
}
return cp(0, -1, p1.data, p2.data)
}
}
func parsePacket(b []byte) *packet {
var parseList func(list []t, b []byte) []t
parseList = func(list []t, b []byte) []t {
for i := 0; i < len(b); i++ {
if b[i] == '[' && b[i+1] == ']' {
list = append(list, []t{})
} else if b[i] == '[' {
j := 1
subchildren := 1
for subchildren > 0 {
if i+j >= len(b) {
break
}
if b[i+j] == '[' {
subchildren += 1
}
if b[i+j] == ']' {
subchildren = subchildren - 1
}
j++
}
list = append(list, parseList([]t{}, b[i+1:i+j-1]))
i = i + j
} else {
j := 0
for ; i+j < len(b); j++ {
stop := false
switch b[i+j] {
case ']':
stop = true
case ',':
stop = true
}
if stop {
break
}
}
s := string(b[i : i+j])
if len(s) == 0 {
s = string(b[len(b)-1])
}
num, err := strconv.Atoi(s)
if err != nil {
continue
}
list = append(list, num)
i = i + j
}
}
return list
}
return &packet{data: parseList([]t{}, b[1:len(b)-1])}
}
func swap(packets []*packet, key, i int) []*packet {
packets[i], packets[key] = packets[key], packets[i]
return packets
}
func quicksort(packets []*packet, comp func(p1, p2 *packet) (int, compcode)) []*packet {
sort.Slice
var qs func(p []*packet)
qs = func(p []*packet) {
key := len(p) - 1
for i := key - 1; i >= 0; i-- {
_, code := comp(p[key], p[i])
if code == rightOrder {
p = swap(p, key, i)
}
}
if key <= 0 || key+1 > len(p) {
return
} else {
left, right := p[:key], p[key+1:]
qs(left)
qs(right)
}
}
qs(packets)
return packets
}
func main() {
f, err := os.Open("day13.txt")
if err != nil {
log.Fatal("Could not read input file")
}
s := bufio.NewScanner(f)
packets := []*packet{}
for s.Scan() {
if len(s.Bytes()) > 0 {
packets = append(packets, parsePacket(s.Bytes()))
}
}
runningSum := 0
comparePackets := newComparePackets(func(a, b int) compcode {
if a == b {
return cont
}
if a < b {
return rightOrder
} else {
return wrongOrder
}
})
for i := 0; i < len(packets); i += 2 {
_, code := comparePackets(packets[i], packets[i+1])
if code == rightOrder {
runningSum += (i / 2) + 1
}
}
fmt.Println("Part 1:", runningSum)
// pick key last element
// sort all elements according to key
// swap key into place
// divide array
// repeat
marker2, marker6 := &packet{[]t{[]t{2}}}, &packet{[]t{[]t{6}}}
packets = append(packets, marker2, marker6)
decoderKey := 1
for i, p := range quicksort(packets, comparePackets) {
if p == marker2 || p == marker6 {
decoderKey *= i + 1
}
}
fmt.Println("Part 2:", decoderKey)
}
|
