feat: add part one solution

internal/2018/DayTwo/code.go

@@ -0,0 +1,49 @@
+package daytwo
+
+import (
+	"advent-of-code/internal/registry"
+	"os"
+	"strings"
+)
+
+func init() {
+	registry.Register("2018D2", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(data []string) int {
+	countWithTwo := 0
+	countWithThree := 0
+
+	for _, boxID := range data {
+		charCounts := make(map[rune]int)
+		for _, char := range boxID {
+			charCounts[char]++
+		}
+
+		hasExactlyTwo := false
+		hasExactlyThree := false
+
+		for _, count := range charCounts {
+			switch count {
+			case 2:
+				hasExactlyTwo = true
+			case 3:
+				hasExactlyThree = true
+			}
+		}
+
+		if hasExactlyTwo {
+			countWithTwo++
+		}
+		if hasExactlyThree {
+			countWithThree++
+		}
+	}
+
+	return countWithTwo * countWithThree
+}