所以，如果输入像s="hel??"，那么输出将是helab，se第一个问号可能是除'l'之外的任何东西，当给出第一个时，第二个可以是除'a'之外的任何东西.
让我们看看以下实现以获得更好的理解-
def solve(s):
if len(s) == 1 :
if s == "?":
return "a"
return s
s = list(s)
for i in range(len(s)):
if s[i] == "?":
if i == 0 and s[i+1] == "?":
s[i] = "a"
elif i == 0 and s[i+1] == "a":
s[i] = "b"
elif i == 0:
s[i] = "a"
elif i == len(s)-1 and s[i-1] == "a":
s[i] = "b"
elif i == len(s)-1:
s[i] = "a"
elif s[i-1] == "a" and s[i+1] == "?":
s[i] = "b"
elif s[i+1] == "?":
s[i] = "a"
elif (s[i-1] == "a" and s[i+1] == "b") or (s[i-1] == "b" and s[i+1] == "a"):
s[i] = "c"
elif "a" in (s[i-1],s[i+1]):
s[i] = "b"
else:
s[i] = "a"
return "".join(s)
s = "hel??"
print(solve(s))"hel??"输出结果
helab