[Python3] one of three letters
\n\nclass Solution:\n    def modifyString(self, s: str) -> str:\n        s = list(s)\n        for i in range(len(s)):\n            if s[i] == "?": \n           
\n```\nclass Solution:\n    def modifyString(self, s: str) -> str:\n        s = list(s)\n        for i in range(len(s)):\n            if s[i] == "?": \n                for c in "abc": \n                    if (i == 0 or s[i-1] != c) and (i+1 == len(s) or s[i+1] != c): \n                        s[i] = c\n                        break \n        return "".join(s)\n```
['Python3']