⚠️ Python 循环列表删除元素的注意事项

 错误示范：

class Solution:
    def removeElement(self, nums, val: int) -> int:
        for i, num in enumerate(nums):
            print('i=', i, ', num=', num, ', nums=', nums)
            if num == val:
                nums.remove(val)
        return len(nums)

s = Solution()
s.removeElement([2, 0,1,2,2,3,0,4,2], 2)
# i= 0 , num= 2 , nums= [2, 0, 1, 2, 2, 3, 0, 4, 2]
# i= 1 , num= 1 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 2 , num= 2 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 3 , num= 3 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 4 , num= 0 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 5 , num= 4 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 6 , num= 2 , nums= [0, 1, 2, 3, 0, 4, 2]

解决方式：

① 使用尾递归方式

class Solution:
    def removeElement(self, nums, val: int) -> int:
        for i, num in enumerate(nums[::-1]):
            print('i=', i, ', num=', num, ', nums=', nums)
            if num == val:
                nums.remove(val)
        return len(nums)

s = Solution()
s.removeElement([2, 0,1,2,2,3,0,4,2], 2)
# i= 0 , num= 2 , nums= [2, 0, 1, 2, 2, 3, 0, 4, 2]
# i= 1 , num= 4 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 2 , num= 0 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 3 , num= 3 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 4 , num= 2 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 5 , num= 2 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 6 , num= 1 , nums= [0, 1, 3, 0, 4, 2]
# i= 7 , num= 0 , nums= [0, 1, 3, 0, 4, 2]
# i= 8 , num= 2 , nums= [0, 1, 3, 0, 4, 2]

 ② 使用 while 循环的方式

class Solution:
    def removeElement(self, nums, val: int) -> int:
        i = 0
        while i < len(nums):
            print('i=', i, ', num=', nums[i], ', nums=', nums)
            if nums[i] == val:
                nums.pop(i)
            else:
                i += 1
        return len(nums)

s = Solution()
s.removeElement([2, 0,1,2,2,3,0,4,2], 2)
# i= 0 , num= 2 , nums= [2, 0, 1, 2, 2, 3, 0, 4, 2]
# i= 0 , num= 0 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 1 , num= 1 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 2 , num= 2 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 2 , num= 2 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 2 , num= 3 , nums= [0, 1, 3, 0, 4, 2]
# i= 3 , num= 0 , nums= [0, 1, 3, 0, 4, 2]
# i= 4 , num= 4 , nums= [0, 1, 3, 0, 4, 2]
# i= 5 , num= 2 , nums= [0, 1, 3, 0, 4, 2]

 ③ 对整个序列使用切片来创建一个临时副本

class Solution:
    def removeElement(self, nums, val: int) -> int:
        for i, num in enumerate(nums[:]):
            print('i=', i, ', num=', num, ', nums=', nums)
            if num == val:
                nums.remove(val)
        return len(nums)

s = Solution()
s.removeElement([2, 0,1,2,2,3,0,4,2], 2)
# i= 0 , num= 2 , nums= [2, 0, 1, 2, 2, 3, 0, 4, 2]
# i= 1 , num= 0 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 2 , num= 1 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 3 , num= 2 , nums= [0, 1, 2, 2, 3, 0, 4, 2]
# i= 4 , num= 2 , nums= [0, 1, 2, 3, 0, 4, 2]
# i= 5 , num= 3 , nums= [0, 1, 3, 0, 4, 2]
# i= 6 , num= 0 , nums= [0, 1, 3, 0, 4, 2]
# i= 7 , num= 4 , nums= [0, 1, 3, 0, 4, 2]
# i= 8 , num= 2 , nums= [0, 1, 3, 0, 4, 2]