ByteDance Coding Question: Merge Accounts by Email

You are given a list of accounts where each account is a list: the first element is a person's name and the rest are their emails. Your task is to merge accounts that belong to the same person — two accounts belong to the same person if they share at least one email — and return each merged account with the name followed by the account's unique, lexicographically sorted emails.

How the interview will flow

• Clarify requirements first: confirm whether names can differ for the same email, whether input contains duplicates, and expected output ordering constraints.
• Propose approaches: a Union-Find (disjoint set) that unions emails within the same account, or build an undirected graph with emails as nodes and run DFS/BFS to gather connected components. Use a hash map to map each email to a name and to map email to its DSU parent or adjacency list.
• Implement: focus on correct data structures, deduplication, sorting, and robust edge-case handling (single-email accounts, identical accounts, empty input).
• Analyze complexity: time dominated by union/find operations and sorting of emails per component; space for hash maps and DSU arrays.

Skill signals you should demonstrate

• Strong use of Hash Tables and Union-Find (or graph traversal) and correct string handling
• Ability to reason about complexity and memory trade-offs
• Attention to edge cases and output formatting (unique and sorted emails)

This question tests practical data-structure design and clean implementation skills commonly asked in coding screens and onsite rounds.