A bitwise implementation in C for the n queens problem.
This was something of a milestone project. In the gruelling entry exams for school 42, on the fourth day (going from no coding experience...) we were asked to attempt to sovle the n queens problem in C without the help of any library functions.
I managed to do it then, but by Jove the code was ugly.
Later as a student, I learnt of bitwise operators. They immediately appealed to me due to their inception-like qualities (it's happening inside a number??). As a first project with bitwise operators, I produced an AI able to pack tetris shapes together in the smallest space possible (see here). In this project, I go back and address the 'n queens' problem with a much more elegant solution involving bitwise operators.
The positions of the queens are not recorded, but instead we make use of three integers to see if it is possible to place a queen in a given row. One integer represents the column conflicts (whether a queen is in that column), another represents the major diagonal conflicts (how the queens' left to right diagonal attacks land on that row), and finally the third represents the minor diagonal conflicts (how the other queens' left diagonal attacks land on that row).
Each integer is updated every time a queen can be placed, and every time we move down a row, the major and minor diagonal conflict integers are shifted to the left and right respectively.
A full explanation of the logic in JS can be seen here.