用一个副本替换一系列子串

For a given word, I want to search for all the substrings that appear next to each other at least 3 times, and replace all of them by only one. I know how to do this when the substring is only one character. For instance, the code below returns "Bah" for the input string "Bahhhhhhh":For a given word, I want to search for all the