COEN 171

Principles of Programming Languages

Winter 2000

First Programming Assignment

Problem Statement: The "N Non-attacking Queens" problem is a classic in the instructional programming area. It exemplifies a common problem solving approach known as "backtracking."

In chess, a Queen may attack along the horizontal rows, the vertical columns, or the diagonals. The N Queens problem is to place N Queens on an NxN chessboard so that no Queen attacks another.

Your assignment is to implement two solutions to the 8 Queens problem, one solution using an iterative approach (that is, one in which the main body of the program is a (possibly nested) loop) and the other using a recursive approach (in which the main body is a recursive procedure). You may use any imperative language of your choice (C, C++, Ada, Java, others) that supports recursion.

Hand in complete source listings for your programs, as well as the results of execution indicating a correct solution to the 8 Queens problem. The output can be a printer listing, a print of an output file, or a screen capture of an interactive session.

Suggestions: You may find one solution, or all solutions (I think there are 92!), whichever is easier.

You may find it easier to debug your programs using a smaller board (say, 4x4) simply to minimize execution time. You may also find it easier to implement a solution that works for any value of N, and then invoke it with a parameter to solve the 8x8 case.

There is no requirement for graphical (or other two-dimensional) output of your solution. A simple list of (row, column) pairs is sufficient.

These are not difficult problems. You might want to take this opportunity to work in an imperative language with which you aren't completely familiar, just to gain some additional experience.

Due Date: January 18, 2000