Rebuild Message from Parts

You are given a list of message parts that were cut from a single original message. Reconstruct the original message by joining the parts in the correct order.

Rules:

• The original message starts with the character A and ends with the character Z.
• Two parts can be joined when the last character of one part equals the first character of the next part.
• When joining two parts, the shared boundary character appears only once in the result. Example: "A--b" + "b--z" -> "A--b--z" (not "A--bb--z").
• The first character of every part is unique among all parts.
• A unique reconstruction is guaranteed.

Examples:

` parts = ["b--Z", "A--b"] result = "A--b--Z"

parts = ["A-x", "x-y", "y-Z"] result = "A-x-y-Z" `

Follow-up Questions:

• What if the parts could be joined in multiple valid ways? How would you detect the ambiguity?
• What if the dataset was streamed instead of given up-front?