added comments and improve readability

main.go

@@ -38,35 +38,48 @@ func main() {
 			continue
 		}
 
-		var fLine, lLine string
+		// forward-scan for spelled digits
+		var forwardReplacedLine, backwardReplacedLine string
 		for i := 0; i < len(line); i++ {
-			fLine += string(line[i])
-			for k, v := range reMap {
-				fLine = strings.ReplaceAll(fLine, k, v)
+			forwardReplacedLine += string(line[i])
+
+			// replace found digit by its non-word counterpart (e.g. "one" -> "1")
+			for key, val := range reMap {
+				forwardReplacedLine = strings.ReplaceAll(forwardReplacedLine, key, val)
 			}
 		}
-		fmt.Println(fLine)
+		fmt.Println(forwardReplacedLine)
 
+		// backward-scan for spelled digits
 		for i := len(line) - 1; i >= 0; i-- {
 			if i == len(line)-1 {
-				lLine = string(line[i])
+				backwardReplacedLine = string(line[i])
 			} else {
-				lLine = string(line[i]) + lLine
+				backwardReplacedLine = string(line[i]) + backwardReplacedLine
 			}
 
-			for k, v := range reMap {
-				lLine = strings.ReplaceAll(lLine, k, v)
+			// replace found digit by its non-word counterpart (e.g. "one" -> "1")
+			for key, val := range reMap {
+				backwardReplacedLine = strings.ReplaceAll(backwardReplacedLine, key, val)
 			}
 		}
-		fmt.Println(lLine)
+		fmt.Println(backwardReplacedLine)
 
-		fMatch := nRegex.FindAllStringSubmatch(fLine, -1)
-		lMatch := nRegex.FindAllStringSubmatch(lLine, -1)
-		first := fMatch[0][0]
-		last := lMatch[len(lMatch)-1:][0][0]
+		// 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 forwardReplacedLine)
+		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)