If the string does not contain any palindromic substrings of lengths 2 and 3, then the string does not contain any palindromic substrings at all.

Iterate from right to left and if it is possible to increase character at index i without creating any palindromic substrings of lengths 2 and 3, then increase it.

After increasing the character at index i, set every character after index i equal to character a. With this, we will ensure that we have created a lexicographically larger string than s, which does not contain any palindromes before index i and is lexicographically the smallest.

Finally, we are just left with a case to fix palindromic substrings, which come after index i. This can be done with a similar method mentioned in the second hint.