class Solution(object):
    def removeElement(self, nums, val):
        left = 0
        right = len(nums) - 1
 
        while left <= right:
            if nums[right] == val:
                right = self.fromRightSlide(nums, val, right)
                continue
            if nums[left] == val:
                nums[left] = '_'
                self.swap(nums, left, right)
                right -= 1
            left += 1
        right = len(nums) - 1
        while len(nums) > 0 and nums[right] == "_" :
            nums.pop()
            right -= 1
 
    def swap(self,nums, i, j):
        temp = nums[i]
        nums[i] = nums[j]
        nums[j] = temp
    def fromRightSlide(self, nums, val, right):
        while right >= 0 and nums[right] == val :
            nums[right] = '_'
            right -= 1
        return right

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