将给出字符串的问号转换成字符小写字母，使其满足回文要求

Write a function solution that,given a string S of length N,returns any palindrome which can be obtained by replacing all of
the question marks in S by lowercase letters (‘a’-‘z).If no
palindrome can be obtained,the function should return the string
“NO”.
A palindrome is a string that reads the same both forwards and
backwards.Some examples of palindromes are:”kayak”,”radar”,
“mom”.
Examples:
1.Given S=”?ab??a”,the function should return “aabbaa”.
2.Given S=”bab??a”,the function should return “NO”.
3.Given S=”?a?”,the function may return “aaa”.It may also
return “zaz”,among other possible answers.
Tes
Assume that:
·N is an integer within the range[1.1,000];
·string S consists only of lowercases letters(‘a’-
‘z)or’?.