Determine Whether Package Weights Can Be Safely Arranged

## Problem Package weights are integers from 0 through 9. Determine whether the packages can be reordered so that the sum of every adjacent pair is strictly less than 10. Return only whether such an ordering exists. ### Function Contract Implement `can_arrange_weights(weights) -> bool`. ### Constraints - `0 <= len(weights) <= 200000`. - Every weight is an integer in `[0,9]`. - Each input occurrence must appear exactly once in the arrangement. - An empty or one-element array is valid. ### Examples - `[9,0,8,1,7]` returns `true`, for example via `9,0,8,1,7`. - `[9,9]` returns `false` because its only adjacent pair sums to 18. ```hint Exploit the tiny value domain A frequency array for the ten possible weights avoids comparison sorting and supports a state or greedy argument over counts. ``` ```hint Focus on incompatible adjacencies Large weights require sufficiently small neighbors; test any greedy placement rule against repeated 8s and 9s. ``` ### Edge Cases - Many copies of one weight may require separators. - Zero can neighbor every allowed weight. - Pairs summing to exactly 10 are invalid.