feat: solve part one building the code digit by digit

internal/2016/DayTwo/code.go

@@ -0,0 +1,57 @@
+package daytwo
+
+import (
+	"advent-of-code/internal/registry"
+	"os"
+	"strings"
+)
+
+func init() {
+	registry.Register("2016D2", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(instructions []string) int {
+	row, column := 1, 1
+
+	keypad := [3][3]int{
+		{1, 2, 3},
+		{4, 5, 6},
+		{7, 8, 9},
+	}
+	code := 0
+
+	for _, line := range instructions {
+		for _, move := range line {
+			switch move {
+			case 'U':
+				if row > 0 {
+					row--
+				}
+			case 'D':
+				if row < 2 {
+					row++
+				}
+			case 'L':
+				if column > 0 {
+					column--
+				}
+			case 'R':
+				if column < 2 {
+					column++
+				}
+			}
+		}
+		code = code*10 + keypad[row][column]
+	}
+
+	return code
+}
+
+func PartTwo(data []string) int {
+	return 0
+}