ZYB is a smart guy. One day he learns a new method for representing trees: Euler tour technique (ETT). You can find more details about ETT on this web page: https://en.wik
ZYB is a smart guy. One day he learns a new method for representing trees: Euler tour technique (ETT). You can find more details about ETT on this web page: https://en.wikipedia.org/wiki/Euler_tour_technique. https://blog.nowcoder.net/n/7afe88dc36ef4649b4de941f08abf576 If we use vertices rather than edges in ETT, then any tree with N N N vertices corresponds to a sequence of length 2N−1 2N-1 2N−1, let's call it the vertex-ETT sequence. In the beginning, ZYB generates a tree (the root of that tree is always 1) and writes down its vertex-ETT sequence. However, he spilt ink onto the paper by mistake and some numbers were covered in ink. Can you help him to restore the sequence?
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