python solution
\tclass Solution:\n\t\tdef modifyString(self, s: str) -> str:\n\t\t\tif s == "?":\n\t\t\t\treturn "a"\n\t\t\tletters = "abcdefghijklmnopqrstuvwxyz"\n\t\t\tres =
\tclass Solution:\n\t\tdef modifyString(self, s: str) -> str:\n\t\t\tif s == "?":\n\t\t\t\treturn "a"\n\t\t\tletters = "abcdefghijklmnopqrstuvwxyz"\n\t\t\tres = ""\n\t\t\tfor i in range(len(s)):\n\t\t\t\tif s[i] != "?":\n\t\t\t\t\tres += s[i]\n\t\t\t\telse:\n\t\t\t\t\tif i == 0:\n\t\t\t\t\t\tfor j in letters:\n\t\t\t\t\t\t\tif j != s[1]:\n\t\t\t\t\t\t\t\tres += j\n\t\t\t\t\t\t\t\tbreak\n\t\t\t\t\telif i == len(s) - 1:\n\t\t\t\t\t\tfor j in letters:\n\t\t\t\t\t\t\tif j != res[i - 1]:\n\t\t\t\t\t\t\t\tres += j\n\t\t\t\t\t\t\t\tbreak\n\t\t\t\t\telse:\n\t\t\t\t\t\tfor j in letters:\n\t\t\t\t\t\t\tif j != res[i - 1] and j != s[i + 1]:\n\t\t\t\t\t\t\t\tres += j\n\t\t\t\t\t\t\t\tbreak\n\t\t\treturn res
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