LeetCode 1304: Find N Unique Integers Sum up to Zero

Meta Data

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Difficulty: easy First Attempt: 2025-07-21

• Submissions: Wrong Answer ×2 → Accepted

Approach

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Place i and -i in pairs (i = 1..n/2): each pair sums to 0 and nothing repeats. When n is odd, add one 0.

My Attempts

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1. Attempt 1 used range(-n//2, n//2 + 1), one number too many for even n (it includes 0). For n = 2 it returned [-1, 0, 1], three numbers.
2. Attempt 2 lowered the upper bound for even n, giving [-1, 0], which does not sum to 0.
3. Generating -n//2..n//2 and removing the middle 0 for even n passed.

Solution

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class Solution:
    def sumZero(self, n: int) -> List[int]:
        res = []
        for i in range(1, n // 2 + 1):
            res += [i, -i]                         # each pair cancels
        if n % 2:
            res.append(0)
        return res

Complexity

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Time O(n), space O(n) for the output.

Mistakes to Avoid

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• With even n there is no room for 0 (it would add a number or force removing another).

Interview Explanation

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I place i and -i in pairs, each summing to 0, for n / 2 pairs, and add a 0 when n is odd. Time O(n).