看似简单，实际上想了挺久的

1）内置api方法

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        while nums1 and nums1[-1] == 0:
            if len(nums1) == m:
                break   
            del nums1[-1]
        nums1 += nums2
        nums1.sort()

2）双指针，哪个小输入哪个，再替换Nums1

temp = []
        p1 = 0
        p2 = 0
        while(p1 < m and p2 < n):
            if (nums1[p1] <= nums2[p2]):
                temp.append(nums1[p1])
                p1 += 1
            else:
                temp.append(nums2[p2])
                p2 += 1
        
        while(p1 < m):
            temp.append(nums1[p1])
            p1 += 1
        while(p2 < n):
            temp.append(nums2[p2])
            p2 += 1
        
        for i in range(0, m + n ):
            nums1[i] = temp[i]

3）从后往前