I have trees coded like this:

A ➜ B ➜ C ➜ -1 ➜ D

A ➜ B ➜ C ➜ -1 ➜ -1 ➜ D

When there is -1, it means that you have to go up one level, so in the first example, B has two children (C and D). In the second example, A has two children (B and D).

My goal is to remove one leaf at a time and get the remaining tree, referring to the first example, there are two leaves (C and D), so what I want to get is:

A ➜ B ➜ D

A ➜ B ➜ C

Referring to the second example, there are always two leaves (C and D), so what I want to get is:

A ➜ B ➜ -1 ➜ D

A ➜ B ➜ C

I've written some intricate code, but it doesn't work for all applications, do you have something in mind, or is there already some library that does this job?

CodePudding user response：

It seems to me that in your notation, a leaf is either a label at the very end of the description, or a label in the context ➜ [X] ➜ -1. In either case, you could remove the leaf:

• if the label is at the end, remove it and the ➜ which precedes it (if there is one) and then repeatedly remove ➜ -1 if that appears at the end of the description.

• If the label is in the context ➜ [X] ➜ -1, remove those four tokens.