python clear and fast solution
\n````\nclass Solution:\n    def modifyString(self, s: str) -> str:\n        a=list(s)+["."]\n        for i in range(len(a)-1):\n            if a[i]=="?":\n    
![image](https://assets.leetcode.com/users/images/66b5c536-5df1-4b41-88bb-5b2586e537ce_1646999808.040217.png)\n````\nclass Solution:\n    def modifyString(self, s: str) -> str:\n        a=list(s)+["."]\n        for i in range(len(a)-1):\n            if a[i]=="?":\n                if a[i+1]!="a" and a[i-1]!="a":\n                    a[i]="a"\n                elif a[i+1]!="b" and a[i-1]!="b":\n                    a[i]="b"\n                elif a[i+1]!="c" and a[i-1]!="c":\n                    a[i]="c"\n            i+=1\n        return "".join(a)[:len(s)]\n
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