Add day 2 solution.

2018/day02-2.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"fmt"
+
+	"internal/util"
+)
+
+func main() {
+	ids := util.ReadInput()
+
+	for _, box1 := range ids {
+		for _, box2 := range ids {
+			diffIndex := -1 // diffIndex doubles as the letter to remove and a 'found' flag
+			for i := range box1 {
+				if box1[i] != box2[i] {
+					if diffIndex != -1 {
+						// If we reach here, we've detected more than one error, so we set
+						// diffIndex back to -1 here to avoid the conditional below this loop.
+						diffIndex = -1
+						break
+					}
+					diffIndex = i
+				}
+			}
+			if diffIndex != -1 {
+				fmt.Printf("%s%s\n", box1[0:diffIndex], box1[diffIndex+1:])
+				return
+			}
+		}
+	}
+}