Broadcast Queue Duplicate Track Purge

A radio station logs its playback queue as the sequence of track IDs in the exact order they were added, before any track has actually played. The same numeric ID can be queued more than once if a listener requests the same track multiple times, and these repeats can land anywhere in the sequence, not necessarily next to each other. Before broadcasting, the producer wants every track whose ID appears more than once anywhere in the logged sequence removed entirely -- every occurrence of that ID, not just the later ones -- leaving only the tracks that were queued exactly once, still in their original relative order.

Input format

• Line 1: a single integer n, the number of entries in the queue.
• Line 2: n space-separated integers, the track IDs in queued order.

Output format

• Line 1: a single integer k, the number of tracks that remain after the purge.
• Line 2: the k remaining track IDs, space-separated, in their original relative order (print an empty line if k is 0).

Constraints

• 1 <= n <= 100000
• 0 <= track ID <= 100000

8
7 3 4 3 7 5 6 5

2
4 6

6
1 2 1 2 1 2

0