283.移动零

1.第一次实现
class Solution:
    def moveZeroes(self, nums) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        num_len = len(nums)
        if not num_len:
            return
        for i in range(num_len-1,-1,-1):
            if nums[i] ==0:
                j = i
                while j+1 < num_len and nums[j+1] !=0:
                    nums[j+1], nums[j] = nums[j],nums[j+1]
                    j +=1

2.两次遍历法

class Solution:
    def moveZeroes(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        n = len(nums)
        j = 0
        for i in range(n):
            if nums[i]:
                nums[j] = nums[i]
                j+=1
        for i in range(j,n):
            nums[i] = 0

3. 双指针

class Solution:
    def moveZeroes(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        n = len(nums)
        left = right = 0 
        while right < n:
            if nums[right]:
                nums[right],nums[left] = nums[left],nums[right]
                left += 1
            right +=1 

class Solution:
    def moveZeroes(self, nums) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        j = 0 # 记录非0元素的位置
        for i in range(len(nums)):
            if nums[i] !=0:
                nums[j] = nums[i]
                if i!= j:
                    nums[i] =0
                j+=1
        print(nums)

5.如果可以开辟新空间，定义一个新数组，非0往前边放，0往后边放(不满足题目要求，仅仅一个思路)

        nums_new = []
        for i in range(len(nums)):
            if nums[i]:
                nums_new.append(nums[i])
        for i in range(len(nums)):
            if  not nums[i]:
                nums_new.append(nums[i])
        nums = nums_new
        print(nums)

6.不推荐时间，时间复杂度高

1.遍历整个数组
2.遇到0删除
3.列表后边追加0
class Solution:
    def moveZeroes(self, nums) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        for i in range(len(nums)):
            if nums[i] ==0:
                nums.remove(0)  #O(n)
                nums.append(0)