Problem: covering holes on a pipe
If you see your position from left=0 to right=length(pipe), you can simply cover your holes from left to right.

When adding a new tube, put the leftmost remaining hole at the leftmost covered position by the tube. Then you cannot waste tube.

For instance with radius 2, a tube centered on pos k covers [k-2, k+2]. Then a tube with leftmost on k covers [k, k+4].

With holes at {2, 4, 5, 7, 9, 11}:
- first hole at 2 => first tube at [2, 6] centered on 4
- next hole at 7 => next tube at [7, 11] centered on 9