WA4, i still don't know why :)
please give me some cool inputs and (optionally) your answers to them.

1234567890
10
jafgl
n
ehlnr
tyz
ru
ja
iad
jadh
pty
yo

ans:ja ehlnr tyz

thank you, i've already found mistakes. now optimizing memory strategy...

the test that tiancaihb give has two possibile solutions:
ja ehlnr tyz
jafgl n ru yo
the first one is shorter so it work fine in my program
but I stil get WA4 and do not know where to look for
mistake. Can someone give me any tip in what cases it work
wrong.

Another test. Mainly to check TLE:
2222223222222222322222 etc.
5
a
aa
afa
aaaa
aafaa

Answer - aaaa aafaa aaaa aa afa aaaa

Answer - aaaa aafaa aaaa aa afa aaaa
Answer - aaaa aafaa aa aaaa afa aaaa