Shelf Position
`widths` is a sorted list of book widths on a shelf. Given a new width `w`, return the index at which it should be inserted to keep the list sorted (if books of that exact width already exist, insert the new one before them). An O(log n) solution is expected, but any correct solution is accepted.
`widths` is a sorted list of book widths on a shelf. Given a new width `w`, return the index at which it should be inserted to keep the list sorted (if books of that exact width already exist, insert the new one before them). An O(log n) solution is expected, but any correct solution is accepted.
