Problem about tree

Question

Hi,everyone,I am just new to java.And now I got a problem with storing the following expression into a binary tree:
The expression is like: ((a/b)+((c-d)*e)) in a txt file.
so,what i want to do is to store variable and operation(+-*/)into a tree.And calculate that by using preorder traversal such as
+(/(a,b),*(-(c,d),e)).However,i even don't know how to start coding.
+
a b - e
c d
the data i want to be stored in a tree will be like above.Then,I need to use inorder traversal to display the final formula like ((a/b)+((c-d)*e))
Please get me some help.Thank you very much from everybody!

Answer 1

Hi,
don't have any code to answer your question but here's what I'll suggest:
1) Define a class whose job will be to represent a simple expression. A simple expression is defined by '<exprX> <operator> <exprY>'. In this class, you must include a way to distinguish expressions from variables.
With your sample, there would be N expressions:
expr1 = (a / b)
expr2 = (c - d)
expr3 = (expr2 * e)
expr4 = (expr1 + expr3)
2) Define a class whose job will be to parse the formula, and create the expressions. The idea would be to find operators, and create expressions on left / right sides of the operators (I agree, it's a little harder than that, but I only have ideas right now...)
Also you'll have to store some kind of 'level info', perhaps here should be the use of the tree, keeping track of each level of computation (expr4 will be at top level, then expr3 under it, then expr2 and expr1)
Use of recursion seems evident here (and seems simple to apply to a tree structure):
- first parse will give expr4 = (expr1 + expr3) (both have to be parsed again)
- second parse will occur on expr1 = (a / b) and expr3 = (expr2 * e) (then expr3 has to be parsed)
- third parse will occur on expr2 = (c - d)
That's my two cents... sorry missing time for more help, try starting with this I'll follow the thread and help more if I can!
Regards.