CSC 101 CompLit, Fall 1996
Merrie Bergmann
Ileana Streinu
Dominique Thiébaut

1. From problems to computer solutions:

Problems -> Methods for solving them -> "Recipes" for general use: Algorithms -> Implementation of the algorithm in some Programming Language -> Program -> Translation of the program into a language understood by the machine (Compiling) -> Loading the program in the memory of the computer -> Execution -> Results.

2. Examples of problems: sorting; searching; finding the shortest way to get from one place to another; playing a game; etc.

3. Visualizing computer algorithms: animated algorithms; Java applets on the Web.

4. Very high-level, complex problems. Example: walking through a simulated environment: steps towards Virtual Reality (video clip).

Example:

Sorting

• sorting a list of names in alphabetic order
• sorting a list of grades in ascending order

Various methods:

• by insertion (the card player's method): Insertion Sort;
• by selecting the minimum from what has not yet been seen yet: Selection Sort;
• by piling them up by size (Bucket sort);
• by splitting in two smaller groups (half the size), sorting the smaller groups then merging them together (Merge Sort).

Understanding the methods:

• "live" animations
• animated algorithms (implemented in Hypercard)
• animated algorithms (implemented in Java and accessible on the Web)

Some sites:

• for sorting algorithms: merge sort, sorting algorithms comparisons.
• for the famous Traveling Salesperson Problem
• for the Eight Queen Problem

Which algorithm is better?

How to compare them? By looking at which one runs faster or uses less memory. Exemplify with two sorting algorithms, by counting the number of elementary operations (comparisons) needed to sort.

How do problems get solved by computers?

• computers have memory, so data can be stored there (e.g. the numbers that need to be sorted). Also, the programs that describe the "method" (algorithm), are also stored in the memory.
• computers do perform only one elementary operation in one unit of time (such as those operations hardwired in the processor, as you did in lab last week: addition, comparison of two numbers, etc.)
• the algorithm is implemented in some programming language that the computer can understand.
• there is a compiler that translates the program into elementary steps that the computer can execute one after another. This is the executable program.
• the program is brought into the memory of the computer and its instructions are executed in sequence all the way to the end of the program.

More about this, next week, in Assembly (a low level language, closest to the one that the machine understands).