Writing and Comparing Algorithms

Abstract

What comes back is a fancy map plus a list of directions which resemble the following: 1. Start at Bristol, BS8 1UB, UK. 2. Head west on B4051 toward A4018; continue to follow B4051. 3. Continue on A4018. 4. Continue on B3129; go through two roundabouts; destination will be on the left. 5. Finish at Bristol, BS8 1LN, UK. The directions have some features worth discussing in more detail. Each line in the directions represents a static description of some active step we should perform while following them. The lines have to be followed, or processed, in order: we start at the first step and once that is complete, move on to the next one. If one of the steps is missed out for example, or we start at the third step instead of the first, the directions do not work. The directions are (fairly) unambiguous. It may help to know that the road B4051 is more usually called Park Street, but line #4 is not "go through some roundabouts"; we should go through exactly two roundabouts. This means it is always clear how to process each line (i.e., exactly what steps to perform): we never become confused because there is not enough information and we do not know what to do. 2.1 Algorithms As a result of the features described above, our directions at least loosely satisfy the definition of an algorithm [1]: they are simply an abstract description of how to solve a problem. Of course in this case the problem is helping someone get from one place to another, but we might just as easily write an algorithm to solve other problems as well.