27. 移除元素

https://leetcode-cn.com/problems/remove-element/

解法一：

用i标记无val区的尾部，即[0:i]是无val的区域；j一次遍历数组，遇到不等于val的就赋给i处，然后i后移

class Solution:
    def removeElement(self, nums: List[int], val: int) -> int:
        i = j = 0
        while j < len(nums):
            if nums[j] != val:
                nums[i] = nums[j]    #无val区扩张
                i += 1    
            j += 1
        return i    #i即为无val区的长度