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| # | Title | Points | Solved | Admin | |
|---|---|---|---|---|---|
There are positions on a circle, numbered from to in clockwise order. The positions are equally spaced.
Exactly of these positions contain a point. You are given the sorted array of these positions.
Find two line segments such that:
If there is no such pair of segments, report that it is impossible.
For each test case, output the answer in one line.
If there is no valid pair of segments, output .
Otherwise, output four distinct integers , meaning that the segment with endpoints and is parallel to the segment with endpoints and .
Each of these four positions must be one of the given points.
If there are multiple valid answers, you may output any of them.
All four points are available. Pair gives sum , and also gives sum — the chords and are parallel.
Only three points are available. The three pairwise sums are , , and — all distinct, so no two chords can be parallel.
Points . Pair and both have sum — the chords and are parallel.
Points . Pair has sum , and also has sum — those two chords are parallel.
Points . The six pairwise sums are — all distinct modulo , so no parallel chords exist.