LeetCode 27: Remove Element

Meta Data

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Difficulty: easy First Attempt: 2022-05-11

• Submissions: Wrong Answer → Accepted ×3

Approach

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A write pointer k (Two Pointers Template 5): copy every value not equal to val to nums[k] and advance. The first k slots are what remains; order does not matter.

My Attempts

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Attempt 1 compared v != nums (a number against the whole list), always true, so nothing was removed: [2], val = 2 returned 1.

Solution

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class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        k = 0
        for x in nums:
            if x != val:
                nums[k] = x
                k += 1
        return k

Complexity

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

Mistakes to Avoid

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• Compare against val.

Interview Explanation

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A write pointer copies values not equal to val to the front in order, and I return the count. Time O(n), space O(1).