Day 5, part 1.

2018/day05-1.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+
+	"internal/util"
+)
+
+func main() {
+	data := util.ReadInputBytes()
+	result := ApplyReactions(data)
+	fmt.Println(len(result))
+}
+
+func ApplyReactions(data []byte) string {
+	result := data
+	changed := true
+
+	for changed {
+		result, changed = React1(result)
+	}
+
+	return string(result)
+}
+
+// React finds substrings of the form "xX" or "Xx" and removes them, returning
+// the resulting bytes.
+func React(data []byte) ([]byte, bool) {
+	result := bytes.Buffer{}
+	changed := false
+
+	for i := 0; i < len(data); i++ {
+		if i < len(data)-1 &&
+			data[i] != data[i+1] &&
+			string(bytes.ToLower([]byte{data[i]})) == string(bytes.ToLower([]byte{data[i+1]})) {
+
+			// we've found a reduction; skip over it without writing
+			//			return append(data[:i], data[i+2:]...), true
+			i++
+			changed = true
+			continue
+		}
+
+		result.WriteByte(data[i])
+	}
+
+	// No changes possible.
+	return result.Bytes(), changed
+}

2018/internal/util/input.go

@@ -2,6 +2,8 @@ package util
 
 import (
 	"bufio"
+	"bytes"
+	"io/ioutil"
 	"os"
 )
 
@@ -22,3 +24,14 @@ func ReadInput() []string {
 
 	return lines
 }
+
+// ReadInputS is like ReadInput, but returns a byte array.
+func ReadInputBytes() []byte {
+	rawData, err := ioutil.ReadFile(os.Args[1])
+
+	if err != nil {
+		panic(err)
+	}
+
+	return bytes.TrimRight(rawData, "\n")
+}