##两道测试题:
For a given string that only contains alphabet characters a-z, if 3 or more consecutive characters are identical, remove them from the string. Repeat this process until there is no more than 3 identical characters sitting besides each other.
Example:
Input: aabcccbbad
Output:
-> aabbbad
-> aaad
-> d
Instead of removing the consecutively identical characters, replace them with a single character that comes before it alphabetically.
Example:
ccc -> b
bbb -> a
Input: abcccbad
Output:
-> abbbad, ccc is replaced by b
-> aaad, bbb is replaced by a
-> d