27. Remove Element -- Python

27. Remove Element

Given an array and a value, remove all instances of that value in-place and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

The order of elements can be changed. It doesn’t matter what you leave beyond the new length.

Example:

Given nums = [3,2,2,3], val = 3,

Your function should return length = 2, with the first two elements of nums being 2.

思路：
本来是准备依次遍历列表，然后遇到 val 就 remove 掉，每一次 remove 只能移除1个数，不过直接用for遍历整个数组进行remove 操作，当列表中的 val 都被移除以后循环还没结束就会报错（列表中没有val, remove函数就会报错列表中没有要移除的数），所以用 count 先数一下 nums 列表中有几个 val，然后循环 count 次，依次remove掉就可以了，比直接遍历列表效率要高。

我的代码：

class Solution:
    def removeElement(self, nums, val):
        """
        :type nums: List[int]
        :type val: int
        :rtype: int
        """
        for i in range(nums.count(val)):
            nums.remove(val)
        return len(nums)