prepare for day 2

.gitignore

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+# Created by https://www.toptal.com/developers/gitignore/api/goland+all,linux,windows
+# Edit at https://www.toptal.com/developers/gitignore?templates=goland+all,linux,windows
+
+### GoLand+all ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio, WebStorm and Rider
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+
+# User-specific stuff
+.idea/**/workspace.xml
+.idea/**/tasks.xml
+.idea/**/usage.statistics.xml
+.idea/**/dictionaries
+.idea/**/shelf
+
+# AWS User-specific
+.idea/**/aws.xml
+
+# Generated files
+.idea/**/contentModel.xml
+
+# Sensitive or high-churn files
+.idea/**/dataSources/
+.idea/**/dataSources.ids
+.idea/**/dataSources.local.xml
+.idea/**/sqlDataSources.xml
+.idea/**/dynamic.xml
+.idea/**/uiDesigner.xml
+.idea/**/dbnavigator.xml
+
+# Gradle
+.idea/**/gradle.xml
+.idea/**/libraries
+
+# Gradle and Maven with auto-import
+# When using Gradle or Maven with auto-import, you should exclude module files,
+# since they will be recreated, and may cause churn.  Uncomment if using
+# auto-import.
+# .idea/artifacts
+# .idea/compiler.xml
+# .idea/jarRepositories.xml
+# .idea/modules.xml
+# .idea/*.iml
+# .idea/modules
+# *.iml
+# *.ipr
+
+# CMake
+cmake-build-*/
+
+# Mongo Explorer plugin
+.idea/**/mongoSettings.xml
+
+# File-based project format
+*.iws
+
+# IntelliJ
+out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Cursive Clojure plugin
+.idea/replstate.xml
+
+# SonarLint plugin
+.idea/sonarlint/
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties
+
+# Editor-based Rest Client
+.idea/httpRequests
+
+# Android studio 3.1+ serialized cache file
+.idea/caches/build_file_checksums.ser
+
+### GoLand+all Patch ###
+# Ignore everything but code style settings and run configurations
+# that are supposed to be shared within teams.
+
+.idea/*
+
+!.idea/codeStyles
+!.idea/runConfigurations
+
+### Linux ###
+*~
+
+# temporary files which can be created if a process still has a handle open of a deleted file
+.fuse_hidden*
+
+# KDE directory preferences
+.directory
+
+# Linux trash folder which might appear on any partition or disk
+.Trash-*
+
+# .nfs files are created when an open file is removed but is still being accessed
+.nfs*
+
+### Windows ###
+# Windows thumbnail cache files
+Thumbs.db
+Thumbs.db:encryptable
+ehthumbs.db
+ehthumbs_vista.db
+
+# Dump file
+*.stackdump
+
+# Folder config file
+[Dd]esktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Windows Installer files
+*.cab
+*.msi
+*.msix
+*.msm
+*.msp
+
+# Windows shortcuts
+*.lnk
+
+# End of https://www.toptal.com/developers/gitignore/api/goland+all,linux,windows
+
+adventofcode
+

02/go.mod

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+module adventofcode
+
+go 1.21

02/main.go

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+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)
+}