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|
package main
import (
"bufio"
"fmt"
"log"
"os"
"regexp"
"strconv"
)
type crates struct {
stacks [][]byte
}
func (c *crates) topCrates() string {
b := make([]byte, len(c.stacks))
for i, stack := range c.stacks {
if len(stack) > 0 {
b[i] = stack[len(stack)-1]
}
}
return string(b)
}
func (c *crates) move(m move) {
// copy slices
from := c.stacks[m.from-1]
to := c.stacks[m.to-1]
for i := 0; i < m.amount; i++ {
pop, popped := from[len(from)-1], from[:len(from)-1]
from = popped
to = append(to, pop)
}
// set slices
c.stacks[m.to-1] = to
c.stacks[m.from-1] = from
}
func (c *crates) moveMultiple(m move) {
// copy slices
from := c.stacks[m.from-1]
to := c.stacks[m.to-1]
pop, from := from[len(from)-m.amount:], from[:len(from)-m.amount]
// push
c.stacks[m.to-1] = append(to, pop...)
// set popped
c.stacks[m.from-1] = from
}
func (c *crates) parseLine(l []byte) {
// by four
for i := 0; i < len(l); i += 4 {
if 'A' <= l[i+1] && l[i+1] <= 'Z' {
// push front: https://github.com/golang/go/wiki/SliceTricks#push-frontunshift
c.stacks[i/4] = append([]byte{l[i+1]}, c.stacks[i/4]...)
}
}
}
func newCargo(s *bufio.Scanner) *crates {
// build cargo
s.Scan()
line := s.Bytes()
//[x].
//1234
cargo := &crates{stacks: make([][]byte, len(line)/4+1)}
cargo.parseLine(line)
for s.Scan() {
line = s.Bytes()
if len(line) == 0 {
break
}
cargo.parseLine(line)
}
return cargo
}
type move struct {
amount int
from int
to int
}
func parseMove(l string) move {
regex := regexp.MustCompile(`move (?P<amount>\d+) from (?P<from>\d+) to (?P<to>\d+)`)
matches := regex.FindStringSubmatch(l)
m := make([]int, 3)
for i, match := range matches[1:] {
matchInt, err := strconv.Atoi(match)
m[i] = matchInt
if err != nil {
log.Fatal("Got unexpected input in move")
}
}
return move{
amount: m[0],
from: m[1],
to: m[2],
}
}
func main() {
f, err := os.Open("day5.txt")
if err != nil {
log.Fatal("Could not open input file")
}
// part 1
scanner := bufio.NewScanner(f)
cargo := newCargo(scanner)
for scanner.Scan() {
l := scanner.Text()
m := parseMove(l)
cargo.move(m)
}
fmt.Println("Part 1:", cargo.topCrates())
f.Seek(0, 0)
// part 2
scanner = bufio.NewScanner(f)
cargo = newCargo(scanner)
for scanner.Scan() {
l := scanner.Text()
m := parseMove(l)
cargo.moveMultiple(m)
}
fmt.Println("Part 2:", cargo.topCrates())
}
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