Description

COMP9021, Session 1, 2015
1 R Building a general tree
Consider a file named tree.txt containing numbers organised as a tree, a number at a depth of N in the tree being preceded with N tabs in the file. The file can also contain any number of lines with nothing but blank lines. Using the module general_tree.py, write a program that reads the contents of the file. If the file does not contain a proper representation of a tree then the program outputs an error message; otherwise, it builds the tree (an instance of GeneralTree()) and prints it out using the same representation as in the file (except for the possible blank lines of course). Here is a possible interaction:
$ python …
$ cat tree.txt
2
3
1
4
5
7
8
9
10
11
12
6
1
$ python exercise_1.py tree.txt does not contain the correct representation of a tree. $ cat tree.txt
2
3
1
4
5
7
8
9
6 $ python exercise_1.py tree.txt does not contain the correct representation of a tree. $ cat tree.txt
2
3
1
4
5
7
8
9
10
11
12
6
$ python exercise_1.py 2
3
1
4
5
7
8
9
10
11
12
6
$
2 Back to fully parenthesised expressions
Modify the second exercise from Lab 9, that deals with arithmetic expressions written in infix, fully parenthesised, and built from natural numbers using the binary +, -, * and / operators, still using a stack but to build an expression tree rather than to evaluate the expression (that is, representing an expression of the form (first_argument operator second_argument) as a tree whose value is operator, and whose left and right nodes are the subtrees that represent first_argument and second_argument, respectively. The function evaluate() is then reimplemented so as to recursively evaluate the expression from the tree. Interacting with this program is exactly as with the program from Lab 9.