元素不为零的列表计算

Question

Let's assume I have a list:

list1 = [16620, 22032, 0, 0, 0, 136813, 137899, 0, 199546, 204804]

I am looking for a new list that subtracts every 'non-zero' value from the following 'non-zero' value, eg 22032-16620, 137899-136813. 'Zero' values will stay untouched. In addition to that, the subtracted 'non-zero' value should change to zero. The output would look something like:

list2 = [0, 5412, 0, 0, 0, 0, 1086, 0, 0, 5258]

Please note that the numbers, the length of the list and its distribution of elements may vary, eg a list could also look like

list1 = [0, 0, 0, 0, 95472, 0, 0, 104538, 0, 0, 0, 0, 187649, 0, 0, 204841, 0, 0, 0, 0, 0, 0, 0, 0]

which should turn into:

list2 = [0, 0, 0, 0, 0, 0, 0, 9066, 0, 0, 0, 0, 0, 0, 0, 17192, 0, 0, 0, 0, 0, 0, 0, 0]

As you can see, the number of elements stays the same for list1 and list2. Also, there is always an even number of 'zero' values and an even number of 'non-zero' values. Help is greatly appreciated!

What I have so far:

from itertools import cycle, chain
list1 = [11545, 15334, 71341, 73861, 0, 0, 170374, 171671]
newlist = [list1[i + 1] - list1[i] for i in range(len(list1)-1)]
list2 = list(chain.from_iterable(zip(newlist[0::2], cycle([int()]))))
print list2

The output print list2 looks like I imagine it to be, yet it won't work for a list that looks like:

list1 = [16620, 22032, 0, 0, 0, 136813, 137899, 0, 199546, 204804]

Answer 1

Copy over, but adjust non-zero values, keeping track of the previous one.

list2 = []
prev = None
for curr in list1:
    if curr:
        if prev:
            curr -= prev
            prev = None
        else:
            prev = curr
            curr = 0
    list2.append(curr)