第四题 http://acm.ashland.edu/2002/Problem-Set/real.pdf
提示
The approach here is to recognize that ambiguous trees only occur when any node does not have a full contingent of children. If a node can have m children but has only n then there are m-choose-n different trees which have the same pre and post order traversals. Applying this recursively to the tree will eventually give you the correct answer. The key thing to know is which node is an ancestor of another.
谁能解释下啊
