LeetCode 283: Move Zeroes

Meta Data

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Difficulty: easy First Attempt: 2022-08-23

• Submissions: Accepted ×2 → Wrong Answer ×2 → Accepted ×2

Approach

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left is where the next non-zero value goes (Two Pointers Template 5). On a non-zero nums[right], swap it with nums[left] and advance left. Non-zero values keep their order and zeros end up at the back.

My Attempts

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It passed in 2022; a 2025 rewrite placed left += 1 outside the if, advancing every step, so nothing moved: [0, 1] stayed [0, 1].

Solution

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class Solution:
    def moveZeroes(self, nums: List[int]) -> None:
        left = 0
        for right in range(len(nums)):
            if nums[right] != 0:
                nums[left], nums[right] = nums[right], nums[left]
                left += 1

Complexity

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

Mistakes to Avoid

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• left += 1 belongs inside the if, advancing only after writing a non-zero value.

Interview Explanation

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left marks where the next non-zero value goes; each non-zero value is swapped there and left advances, pushing zeros back. Time O(n), space O(1).