feat: Implement 2024 day 2 part 1

Author: obalunenko

internal/puzzles/solutions/2024/day02/solution.go

@@ -2,9 +2,14 @@
 package day02
 
 import (
+	"bufio"
+	"bytes"
+	"fmt"
 	"io"
+	"strconv"
 
 	"github.com/obalunenko/advent-of-code/internal/puzzles"
+	"github.com/obalunenko/advent-of-code/internal/puzzles/common/utils"
 )
 
 func init() {
@@ -22,9 +27,67 @@ func (s solution) Day() string {
 }
 
 func (s solution) Part1(input io.Reader) (string, error) {
-	return "", puzzles.ErrNotImplemented
+	scanner := bufio.NewScanner(input)
+
+	isSafe := func(line []int) bool {
+		var asc, desc bool
+
+		for i, val := range line {
+			if i == 0 {
+				continue
+			}
+
+			if line[i-1] < val {
+				if desc {
+					return false
+				}
+
+				asc = true
+			}
+
+			if line[i-1] > val {
+				if asc {
+					return false
+				}
+
+				desc = true
+			}
+
+			diff := val - line[i-1]
+			if diff < 0 {
+				diff = -diff
+			}
+
+			if diff < 1 || diff > 3 {
+				return false
+			}
+		}
+
+		return true
+	}
+
+	var safeCount int
+
+	for scanner.Scan() {
+		line := scanner.Bytes()
+
+		numbers, err := utils.ParseInts(bytes.NewReader(line), " ")
+		if err != nil {
+			return "", fmt.Errorf("failed to parse input line: %w", err)
+		}
+
+		if isSafe(numbers) {
+			safeCount++
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return "", fmt.Errorf("failed to read input: %w", err)
+	}
+
+	return strconv.Itoa(safeCount), nil
 }
 
-func (s solution) Part2(input io.Reader) (string, error) {
+func (s solution) Part2(_ io.Reader) (string, error) {
 	return "", puzzles.ErrNotImplemented
 }