LeetCode 3688: Bitwise OR of Even Numbers in an Array

Meta Data

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Difficulty: easy First Attempt: 2025-09-21

• Submissions: Accepted (first try)

Approach

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Even numbers have lowest bit 0; OR them all together (Bit Manipulation Template 1). OR starts from 0, which stays untouched when there are no even numbers, exactly the required 0.

My Solution

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class Solution:
    def evenNumberBitwiseORs(self, nums: List[int]) -> int:
        res = 0
        for x in nums:
            if x % 2 == 0:
                res |= x
        return res

I originally filtered first and special-cased an empty list; starting from 0 removes the special case.

Complexity

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

Mistakes to Avoid

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• The identity for OR is 0 and for AND is -1; do not mix them up.

Interview Explanation

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I OR only the even numbers starting from 0; with none, the result is naturally 0. Time O(n).