LeetCode 2413: Smallest Even Multiple

Meta Data

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Difficulty: easy First Attempt: 2025-12-17

• Submissions: Accepted (Python) → Wrong Answer (C++) → Accepted (C++)

Approach

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The smallest positive multiple of both 2 and n is lcm(2, n):

• Even n: n is already a multiple of 2, so the answer is n.
• Odd n: gcd(2, n) = 1, so the answer is 2n.

My Attempts

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Python passed first. Practicing in C++, I swapped the ternary branches: (n % 2) ? n : n * 2 returns n when n % 2 is 1 (odd). For n = 5 the answer is 10; it returned 5.

Solution

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class Solution:
    def smallestEvenMultiple(self, n: int) -> int:
        return n if n % 2 == 0 else 2 * n

Complexity

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Time O(1), space O(1).

Mistakes to Avoid

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• n % 2 is truthy (1) for odd numbers; writing n % 2 == 0 makes the branches harder to swap.

Interview Explanation

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The answer is the least common multiple of 2 and n: n itself when even, and 2n when odd since 2 and n are then coprime. Time O(1).