F2. Tree of Life (medium)

хугацааны хязгаарлалт 5 секунд

санах ойн хязгаарлалт 256 мегабайт

оролт стандарт оролт

гаралт стандарт гаралт

Heidi got tired of deciphering the prophecy hidden in the Tree of Life and decided to go back to her headquarters, rest a little and try there. Of course, she cannot uproot the Tree and take it with her, so she made a drawing of the Tree on a piece of paper. On second thought, she made more identical drawings so as to have n in total (where n is the number of vertices of the Tree of Life) – who knows what might happen?

Indeed, on her way back Heidi was ambushed by a group of zombies. While she managed to fend them off, they have damaged her drawings in a peculiar way: from the i-th copy, the vertex numbered i was removed, along with all adjacent edges. In each picture, the zombies have also erased all the vertex numbers and relabeled the remaining n - 1 vertices arbitrarily using numbers 1 to n (fortunately, each vertex still has a distinct number). What's more, the drawings have been arbitrarily shuffled/reordered.

Now Heidi wants to recover the Tree of Life from her descriptions of all the drawings (as lists of edges).

Оролт

The first line of the input contains Z ≤ 20 – the number of test cases. Z descriptions of single test cases follow.

In each test case, the first line of input contains numbers n (2 ≤ n ≤ 100) and k (where k is the number of drawings; we have k = n). In the following lines, the descriptions of the k drawings are given. The description of the i-th drawing is a line containing mi – the number of edges in this drawing, followed by mi lines describing edges, each of which contains two space-separated integers –- the numbers of the two vertices connected by the edge.

Гаралт

If Heidi's drawings cannot possibly come from a single tree, you should output the word NO. Otherwise, output one line containing the word YES and n - 1 lines describing any tree that Heidi's drawings could have come from. For every edge you should output the numbers of the vertices that it connects, separated with a single space. If there are many solutions, print any of them.

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Жишээ тэстүүд

Оролт
1
5 5
2
4 1
2 1
1
3 1
3
4 1
4 3
2 1
3
3 1
3 2
4 1
3
2 1
3 2
4 2
Гаралт
YES
2 5
4 2
3 2
5 1
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