LeetCode 929: Unique Email Addresses ·

Table of Contents

Meta Data
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Difficulty: easy First Attempt: 2022-09-26

Submissions: Runtime Error → Wrong Answer ×3 → Accepted ×2

Approach
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Normalize each address into a set (Hash Table Template 5): split at @ into local and domain, cut the local part at the first +, then remove every .; leave the domain alone. Put the @ back when rejoining, or different addresses can produce the same string.

My Attempts
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Attempt 1 misspelled replace (AttributeError).
The next two rejoined with "".join(email), dropping the @: ["a@bx.com", "ab@x.com"] both became "abx.com", so the answer 2 came out as 1.
The one after wrote emails[0] + '@' + emails[1], mixing up email and emails, and raised IndexError with a single address.

Solution
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class Solution:
    def numUniqueEmails(self, emails: List[str]) -> int:
        seen = set()
        for e in emails:
            local, domain = e.split("@")
            local = local.split("+")[0].replace(".", "")
            seen.add(local + "@" + domain)
        return len(seen)

Complexity
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Time O(total characters), space O(total characters).

Mistakes to Avoid
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The rules apply only to the local part; keep the domain’s dots.
Keep the @ when rejoining: "a@bx.com" and "ab@x.com" are different addresses.

Interview Explanation
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I split each address at @, cut the local part at + and drop its dots, keep the domain, rejoin, and count distinct results with a set. Time is linear in the total length.