prepare for day 2

01/main.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var (
+	inputFile = flag.String("input", "input.txt", "input filename")
+	nRegex    = regexp.MustCompile(`(?m)\d`)
+	reMap     = map[string]string{
+		"one":   "1",
+		"two":   "2",
+		"three": "3",
+		"four":  "4",
+		"five":  "5",
+		"six":   "6",
+		"seven": "7",
+		"eight": "8",
+		"nine":  "9",
+	}
+)
+
+func main() {
+	flag.Parse()
+	input, err := os.ReadFile(*inputFile)
+	if err != nil {
+		panic(err)
+	}
+
+	var sum int
+	for _, line := range strings.Split(string(input), "\n") {
+		if strings.TrimSpace(line) == "" {
+			continue
+		}
+
+		// forward-scan for spelled digits
+		var forwardReplacedLine, backwardReplacedLine string
+		for i := 0; i < len(line); i++ {
+			forwardReplacedLine += string(line[i])
+
+			// replace all potential spelled out digits by their non-word counterpart (e.g. "one" -> "1")
+			for key, val := range reMap {
+				forwardReplacedLine = strings.ReplaceAll(forwardReplacedLine, key, val)
+			}
+		}
+		fmt.Println(forwardReplacedLine)
+
+		// backward-scan for spelled digits
+		for i := len(line) - 1; i >= 0; i-- {
+			if i == len(line)-1 {
+				backwardReplacedLine = string(line[i])
+			} else {
+				backwardReplacedLine = string(line[i]) + backwardReplacedLine
+			}
+
+			// replace all potential spelled out digits by their non-word counterpart (e.g. "one" -> "1")
+			for key, val := range reMap {
+				backwardReplacedLine = strings.ReplaceAll(backwardReplacedLine, key, val)
+			}
+		}
+		fmt.Println(backwardReplacedLine)
+
+		// find single digits in forward-replaced line
+		firstMatch := nRegex.FindAllStringSubmatch(forwardReplacedLine, -1)
+
+		// find single digits in backward-replaced line
+		lastMatch := nRegex.FindAllStringSubmatch(backwardReplacedLine, -1)
+
+		// get first matchgroup, first match (aka first digit in forwardReplacedLine)
+		first := firstMatch[0][0]
+
+		// get last matchgroup, first match (aka last digit in backwardReplacedLine)
+		last := lastMatch[len(lastMatch)-1:][0][0]
+
+		fmt.Println(first + last)
+
+		// concatenate digits and convert the resulting string to int
+		asInt, err := strconv.Atoi(first + last)
+		if err != nil {
+			panic(err)
+		}
+
+		sum += asInt
+	}
+
+	fmt.Println(sum)
+}