feat: Implement 2018/day02 (#53)

* feat: Initial commit for 2018/day02

* feat: Implement 2018/day02 part1

* fix: Add scanner error handling

* docs: Add 2018/day02 part2 spec

* chore: Remove input file

* feat: Implement 2018/day02 part2

* chore: Cleanup 2018/day02

* chore: Add regression test for 2018/day02 part2

* docs: Mark 2018/day02 as solved

Author: obalunenko

README.md

@@ -125,7 +125,7 @@ This repository contains solutions for puzzles and cli tool to run solutions to
   <summary>2018</summary>  
 
   - [x] [Day 1: Chronal Calibration](https://adventofcode.com/2018/day/1)
-  - [ ] [Day 2: Inventory Management System](https://adventofcode.com/2018/day/2)
+  - [x] [Day 2: Inventory Management System](https://adventofcode.com/2018/day/2)
   - [ ] [Day 3: No Matter How You Slice It](https://adventofcode.com/2018/day/3)
   - [ ] [Day 4: Repose Record](https://adventofcode.com/2018/day/4)
   - [ ] [Day 5: Alchemical Reduction](https://adventofcode.com/2018/day/5)

internal/puzzles/solutions/2017/day02/solution.go

@@ -126,5 +126,9 @@ func findChecksum(spreadsheet io.Reader, f checksumFunc) (string, error) {
 		checksum += n
 	}
 
+	if err := scanner.Err(); err != nil {
+		return "", fmt.Errorf("scanner error: %w", err)
+	}
+
 	return strconv.Itoa(checksum), nil
 }

internal/puzzles/solutions/2018/day02/solution.go

@@ -0,0 +1,172 @@
+// Package day02 contains solution for https://adventofcode.com/2018/day/2 puzzle.
+package day02
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/obalunenko/advent-of-code/internal/puzzles"
+)
+
+func init() {
+	puzzles.Register(solution{})
+}
+
+type solution struct{}
+
+func (s solution) Day() string {
+	return puzzles.Day02.String()
+}
+
+func (s solution) Year() string {
+	return puzzles.Year2018.String()
+}
+
+func (s solution) Part1(input io.Reader) (string, error) {
+	boxes, err := makeBoxesList(input)
+	if err != nil {
+		return "", fmt.Errorf("make boxes: %w", err)
+	}
+
+	const (
+		two   = 2
+		three = 3
+	)
+
+	var (
+		twoCount, threeCount int
+	)
+
+	for i := range boxes {
+		box := boxes[i]
+
+		if hasNSameLetters(box, two) {
+			twoCount++
+		}
+
+		if hasNSameLetters(box, three) {
+			threeCount++
+		}
+	}
+
+	checksum := twoCount * threeCount
+
+	return strconv.Itoa(checksum), nil
+}
+
+var errNotFound = errors.New("not found")
+
+func (s solution) Part2(input io.Reader) (string, error) {
+	boxes, err := makeBoxesList(input)
+	if err != nil {
+		return "", fmt.Errorf("make boxes: %w", err)
+	}
+
+	// finds same boxes
+	// find common letters
+	boxesnum := len(boxes)
+
+	var (
+		box1, box2, common string
+	)
+
+loop:
+	for i := 0; i <= boxesnum; i++ {
+		for j := i + 1; j <= boxesnum-1; j++ {
+			if hasNDiffLetters(boxes[i], boxes[j], 1) {
+				box1, box2 = boxes[i], boxes[j]
+
+				common = getCommonBoxesPart(box1, box2)
+
+				break loop
+			}
+		}
+	}
+
+	if common == "" {
+		return "", errNotFound
+	}
+
+	return common, nil
+}
+
+func getCommonBoxesPart(box1, box2 string) string {
+	if len(box1) != len(box2) {
+		return ""
+	}
+
+	br1, br2 := []rune(box1), []rune(box2)
+
+	common := make([]rune, 0, len(br1))
+
+	for i := 0; i < len(br1); i++ {
+		a, b := br1[i], br2[i]
+		if a == b {
+			common = append(common, a)
+		}
+	}
+
+	return string(common)
+}
+
+func hasNDiffLetters(box1, box2 string, n int) bool {
+	if n < 0 {
+		return false
+	}
+
+	if len(box1) != len(box2) {
+		return false
+	}
+
+	var diff int
+
+	for i := 0; i < len(box1); i++ {
+		if box1[i] == box2[i] {
+			continue
+		}
+
+		diff++
+	}
+
+	return diff == n
+}
+
+func makeBoxesList(input io.Reader) ([]string, error) {
+	var boxes []string
+
+	scanner := bufio.NewScanner(input)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		boxes = append(boxes, line)
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("scanner error: %w", err)
+	}
+
+	return boxes, nil
+}
+
+func hasNSameLetters(s string, n int) bool {
+	if n <= 0 {
+		return false
+	}
+
+	seen := make(map[rune]int)
+
+	for _, c := range s {
+		seen[c]++
+	}
+
+	for _, i := range seen {
+		if i == n {
+			return true
+		}
+	}
+
+	return false
+}