class Solution:
def modifyString(self, s: str) -> str:
res = list(s)
n = len(res)
for i in range(n):
if res[i] == '?':
for b in "abc":
if not (res[i - 1] == b or i < n - 1 and res[i + 1] == b):
res[i] = b
break
return "".join(res)
Q.E.D.