feat: Implement part 1

internal/puzzles/solutions/2023/day01/solution.go

@@ -2,7 +2,11 @@
 package day01
 
 import (
+	"bufio"
+	"fmt"
 	"io"
+	"strconv"
+	"unicode"
 
 	"github.com/obalunenko/advent-of-code/internal/puzzles"
 )
@@ -21,8 +25,66 @@ func (s solution) Day() string {
 	return puzzles.Day01.String()
 }
 
-func (s solution) Part1(_ io.Reader) (string, error) {
-	return "", puzzles.ErrNotImplemented
+func (s solution) Part1(input io.Reader) (string, error) {
+	scanner := bufio.NewScanner(input)
+
+	var values []int
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+
+		first, last := -1, -1
+
+		for _, c := range line {
+			if !unicode.IsDigit(c) {
+				continue
+			}
+
+			if first == -1 {
+				d, err := strconv.Atoi(string(c))
+				if err != nil {
+					return "", fmt.Errorf("failed to convert %s to int: %w", string(c), err)
+				}
+
+				first = d
+			}
+
+			if first != -1 {
+				d, err := strconv.Atoi(string(c))
+				if err != nil {
+					return "", fmt.Errorf("failed to convert %s to int: %w", string(c), err)
+				}
+
+				last = d
+			}
+		}
+
+		if last == -1 {
+			last = first
+		}
+
+		value, err := strconv.Atoi(strconv.Itoa(first) + strconv.Itoa(last))
+		if err != nil {
+			return "", fmt.Errorf("failed to convert %d%d to int: %w", first, last, err)
+		}
+
+		values = append(values, value)
+	}
+
+	if err := scanner.Err(); err != nil {
+		return "", fmt.Errorf("reading input: %w", err)
+	}
+
+	var sum int
+
+	for _, v := range values {
+		sum += v
+	}
+
+	return strconv.Itoa(sum), nil
 }
 
 func (s solution) Part2(_ io.Reader) (string, error) {