Multi-Account Cheating

01 · Question

Each user has an unordered list of IP addresses they have connected from. Return whether two users have exactly the same IP addresses.

Example:

Input: [("mike", ["203.0.113.10"]), ("bob", ["222.0.0.5", "111.0.0.10"]), ("bob2", ["111.0.0.10", "222.0.0.5"])]
Output: true

02 · Analysis

The same IPs may appear in different orders. Sort each user's IPs and convert the result to one immutable canonical key. Equal unordered lists now produce equal keys, so a set detects duplicates.

If a user has $k$ IPs, canonicalizing that list costs $O(k log k)$ . The set stores one signature per user in the worst case.

03 · Solution

Reference solution

1def multi_account_cheating(users):
2    seen = set()
3
4    for _, ips in users:
5        signature = tuple(sorted(ips))
6        if signature in seen:
7            return True
8        seen.add(signature)
9
10    return False

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