ZOJ Problem Set - 1097
A tree (i.e. a connected graph without cycles) with vertices numbered by
the integers 1, 2, ..., n is given. The "Prufer" code of
such a tree is built as follows: the leaf (a vertex that is incident to only
one edge) with the minimal number is taken. This leaf, together with its
incident edge is removed from the graph, while the number of the vertex
that was adjacent to the leaf is written down. In the obtained graph, this
procedure is repeated, until there is only one vertex left (which, by the
way, always has number n). The written down sequence of n-1
numbers is called the Prufer code of the tree.
T ::= "(" N S ")" S ::= " " T S | empty N ::= numberThat is, trees have parentheses around them, and a number denoting the identifier of the root vertex, followed by arbitrarily many (maybe none) subtrees separated by a single space character. As an example, take a look at the tree in the figure below which is denoted in the first line of the sample input.
Note that, according to the definition given above, the root of a tree may be a leaf as well. It is only for the ease of denotation that we designate some vertex to be the root. Usually, what we are dealing here with is called an "unrooted tree".
The input contains several test cases. Each test case specifies a tree as described above on one line of the input file. Input is terminated by EOF. You may assume that 1<=n<=50.
For each test case generate a single line containing the Prufer code of the specified tree. Separate numbers by a single space. Do not print any spaces at the end of the line.
Source: University of Ulm Local Contest 2001