147 lines
2.9 KiB
Go
147 lines
2.9 KiB
Go
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"io"
|
|
"os"
|
|
"strconv"
|
|
"strings"
|
|
"unicode"
|
|
)
|
|
|
|
type Coordinate struct {
|
|
row int
|
|
col int
|
|
}
|
|
|
|
func main() {
|
|
if len(os.Args) != 2 {
|
|
fmt.Fprintf(os.Stderr, "Usage: %s inputfile\n", os.Args[0])
|
|
os.Exit(1)
|
|
}
|
|
|
|
filename := os.Args[1]
|
|
inputFile, err := os.Open(filename)
|
|
if err != nil {
|
|
panic(fmt.Sprintf("failed to open input file: %s", err))
|
|
}
|
|
|
|
inputBytes, err := io.ReadAll(inputFile)
|
|
if err != nil {
|
|
panic(fmt.Sprintf("failed to read input file: %s", err))
|
|
}
|
|
|
|
input := string(inputBytes)
|
|
inputLines := strings.Split(strings.TrimSpace(input), "\n")
|
|
|
|
fmt.Printf("Part 1: %d\n", part1(inputLines))
|
|
}
|
|
|
|
func part1(inputLines []string) int {
|
|
symbolPositions := findSymbols(inputLines)
|
|
partNumberCandidates := []Coordinate{}
|
|
for _, symbolPos := range symbolPositions {
|
|
candidates := findNumbersAdjacentTo(inputLines, symbolPos)
|
|
partNumberCandidates = append(partNumberCandidates, candidates...)
|
|
}
|
|
|
|
total := 0
|
|
scanned := map[Coordinate]struct{}{}
|
|
for _, candidate := range partNumberCandidates {
|
|
if _, ok := scanned[candidate]; ok {
|
|
continue
|
|
}
|
|
|
|
line := inputLines[candidate.row]
|
|
|
|
backwardsBuf := strings.Builder{}
|
|
// Scan backward
|
|
for i := candidate.col - 1; i >= 0; i-- {
|
|
char := line[i]
|
|
if !unicode.IsDigit(rune(char)) {
|
|
break
|
|
}
|
|
|
|
scanned[Coordinate{row: candidate.row, col: i}] = struct{}{}
|
|
backwardsBuf.WriteByte(char)
|
|
}
|
|
|
|
forwardsBuf := strings.Builder{}
|
|
// Scan forward
|
|
for i := candidate.col; i < len(line); i++ {
|
|
char := line[i]
|
|
if !unicode.IsDigit(rune(char)) {
|
|
break
|
|
}
|
|
|
|
scanned[Coordinate{row: candidate.row, col: i}] = struct{}{}
|
|
forwardsBuf.WriteByte(char)
|
|
}
|
|
|
|
fullNumber := reverseString(backwardsBuf.String()) + forwardsBuf.String()
|
|
scannedNumber, err := strconv.Atoi(fullNumber)
|
|
if err != nil {
|
|
panic(fmt.Sprintf("%s was not a number", fullNumber))
|
|
}
|
|
|
|
total += scannedNumber
|
|
}
|
|
|
|
return total
|
|
}
|
|
|
|
func findSymbols(inputLines []string) []Coordinate {
|
|
coords := []Coordinate{}
|
|
for row, line := range inputLines {
|
|
for col, char := range line {
|
|
if isSymbol(char) {
|
|
coord := Coordinate{
|
|
row: row,
|
|
col: col,
|
|
}
|
|
|
|
coords = append(coords, coord)
|
|
}
|
|
}
|
|
}
|
|
|
|
return coords
|
|
}
|
|
|
|
func findNumbersAdjacentTo(inputLines []string, coordinate Coordinate) []Coordinate {
|
|
coords := []Coordinate{}
|
|
for dRow := -1; dRow <= 1; dRow++ {
|
|
for dCol := -1; dCol <= 1; dCol++ {
|
|
if dRow == 0 && dCol == 0 {
|
|
continue
|
|
}
|
|
|
|
row := coordinate.row + dRow
|
|
col := coordinate.col + dCol
|
|
if unicode.IsDigit(rune(inputLines[row][col])) {
|
|
coord := Coordinate{
|
|
row: row,
|
|
col: col,
|
|
}
|
|
|
|
coords = append(coords, coord)
|
|
}
|
|
}
|
|
}
|
|
|
|
return coords
|
|
}
|
|
|
|
func isSymbol(r rune) bool {
|
|
return r != '.' && !unicode.IsDigit(r)
|
|
}
|
|
|
|
func reverseString(s string) string {
|
|
buffer := strings.Builder{}
|
|
for i := len(s) - 1; i >= 0; i-- {
|
|
buffer.WriteByte(s[i])
|
|
}
|
|
|
|
return buffer.String()
|
|
}
|