A trick to move a prefix of any length to the end of an array, in place:

Say k is the length of the prefix.

1. Reverse the array.
2. Reverse the final k elements.
3. Reverse the remaining elements.

For instance, if we have "outbreak" and we need to move "out" to the end:

1. reverse the whole thing to get "kaerbtuo"
2. reverse the final three letters to get "kaerbout"
3. reverse the first five letters to get "breakout"