Algorithms and OOD (CSC 207 2013F) : Labs

# Laboratory: Stacks

Summary: In this laboratory, you will have an opportunity to ground your understanding of stacks, particularly of the array-based implementation of stacks.

Required Code Files:

## Preparation

a. Review the reading on linear structures.

b. Review the reading on stacks.

c. Fork and clone the repo at https://github.com/Grinnell-CSC207/linear

## Exercises

### Exercise 1: Basic Experiments

Read through `LSExpt.java` and `LinkedStackExpt`. Summarize what the stack should look like at each step. (A piece of paper might help.) Note that the `info` method will print information on the stack (is it empty? is it full? what elements are in the stack) and the `clear` method will repeatedly call `get` until the stack is empty.

Run `LinkedStackExpt` and see if you get the output that you expect.

### Exercise 2: A Wrapper Class

Skim through `ReportingLinearStructure.java`. Summarize the main approach of the class. What ideas from the class might you apply in other situations? (Pick at least one or two.)

### Exercise 3: A Faulty Implementation

The file `ArrayBasedStack.java` has a significant bug. Identify and correct that bug.

### Exercise 4: Matching Parens

One useful application of stacks is matching things. For example, we can match the parens in a Scheme expression as follows:

Step through the characters in the expression
When you encounter an open paren or open square bracket, push it
on the stack
When you encounter a close paren or close square bracket, pop
the corresponding opening character off the stack.  If the two
characters don't match, issue an error.
If you encounter a closing character with an empty stack, that
close paren or bracket is mismatched.
If the stack is not empty, there are unmatched open or closed parens.

Implement this algorithm. (You might also add support for braces and angle brackets.) That is, write and experiment with a method, `checkMatching(String str)`, that checks whether the parens, square brackets, and potentially other characters, match correctly.

## For Those with Extra Time

### Extra 1: Matching, Revisited

Revise your answer from the previous exercise to store the indices of matching symbols. That is, you will need to push both symbol and index. Use the indices to provide better error messages (e.g., you can say where the mismatch occurs in the string).

How can you store two kinds of values in stack? One option is to make it a stack of Objects, and alternately push Character and Integer objects. Another option is to create a simple class that groups a character and an integer.

### Extra 2: Displaying Matching Parens

Extend your answer from the previous extra problem to provide a nice picture of the matching parens. For example, for each pair of matching parens, you might draw a line underneath, as in the following.

```(oh (boy) (I am having) ((so) much) fun matching (parens))
+---+
+-----------+
+--+
+---------+
+------+
+--------------------------------------------------------+
```

Copyright (c) 2013 Samuel A. Rebelsky.

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