> For the complete documentation index, see [llms.txt](https://garylai.gitbook.io/algorithm-and-data-structure/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://garylai.gitbook.io/algorithm-and-data-structure/problems/two-pointers/remove-element.md).

# 27. Remove Element

[27. Remove Element](https://leetcode.com/problems/remove-element/)

要從兩個方向看

1. 如果現在最右邊的指針，當下的值和 val 相同，想辦法往左邊移，移動到和 val 不同即可停止。
2. 如果左邊的指針指到的值剛好和 val 相同，將這個值往後面丟（和右邊指針的值交換）

```python
class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        left = 0
        right = len(nums) - 1

        while left < right:
            while nums[right] == val and left < right:
                right -= 1
            if nums[left] == val:
                nums[left], nums[right] = nums[right], nums[left]
            left += 1

        return sum([1 for num in nums if num != val])
```