题解 | #数位dp？#

双端队列，从前往后遍历，把前导零去掉，从后往前遍历，把末位奇数去掉。记录一下初始长度和最后长度，相减得到答案。

from collections import deque
a = deque(input().strip())
oldlena = len(a)
lena = len(a)
while lena > 0:
    if a[0] == "0" and lena!=1:
        a.popleft()
        lena -= 1
    else:
        break
while lena > 0:
    if a[~0] not in {"0","2","4","6","8"}:
        a.pop()
        lena -= 1
    else:
        break
print(oldlena-lena)