Implementation for 5A

aoc2018.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"time"
 
+	"github.com/nlowe/aoc2018/day5"
+
 	"github.com/nlowe/aoc2018/day4"
 
 	"github.com/nlowe/aoc2018/day3"
@@ -43,6 +45,7 @@ func main() {
 		day2.A, day2.B,
 		day3.A, day3.B,
 		day4.A, day4.B,
+		day5.A,
 	)
 
 	flags := rootCmd.PersistentFlags()

day5/a.go

@@ -0,0 +1,52 @@
+package day5
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/nlowe/aoc2018/util"
+	"github.com/spf13/cobra"
+)
+
+var A = &cobra.Command{
+	Use:   "5a",
+	Short: "Day 5, Problem A",
+	Run: func(_ *cobra.Command, _ []string) {
+		fmt.Printf("Answer: %d\n", a(util.ReadInput()))
+	},
+}
+
+const delta = 'a' - 'A'
+
+func intAbs(a int32) int32 {
+	return (a + (a >> 31)) ^ (a >> 31)
+}
+
+func a(input *util.ChallengeInput) int {
+	polymer := <-input.Lines()
+
+	for {
+		buff := strings.Builder{}
+		reduced := false
+
+		for i := 0; i < len(polymer)-1; i++ {
+			if intAbs(rune(polymer[i])-rune(polymer[i+1])) == delta {
+				i++
+				reduced = true
+			} else {
+				buff.WriteRune(rune(polymer[i]))
+
+				if i == len(polymer)-2 {
+					buff.WriteRune(rune(polymer[i+1]))
+				}
+			}
+		}
+
+		polymer = buff.String()
+		if !reduced {
+			break
+		}
+	}
+
+	return len(polymer)
+}

day5/a_test.go

@@ -0,0 +1,14 @@
+package day5
+
+import (
+	"testing"
+
+	"github.com/nlowe/aoc2018/util"
+	"github.com/stretchr/testify/require"
+)
+
+func TestA(t *testing.T) {
+	input := util.TestInput(`dabAcCaCBAcCcaDA`)
+
+	require.Equal(t, 10, a(input))
+}