Narcissistic numbers

Here is a nice mathematical exercise from Programming Praxis. Is about finding the “narcissistic numbers”, n digit numbers numbers where the sum of all the nth power of their digits is equal to the number. To reduce the problem a little, I decided to start by limiting the number of digits. So, the first approach will be just calculate if a number is narcissistic of not. So, after checking it and making a couple of performance adjustments, the code is as follows…

Travelling salesman

One classic computation problem, the travelling salesman. Even if it’s quite simple to describe, it’s one of those hideous NP complete problems, the ones that are quite difficult to resolve, as the computation time needed grows greatly with the length of the data. On Programming Praxis they have proposed to resolve the problem using brute force, and using the closest neighbor (a simplification of the problem). I’ve created this program, in Python. The time spend on each is brutally different, specially as the number of cities grow. With more than 9 cities,… Read More

\$7.11 in four prices and the Decimal type

There’s an fun and not very difficult programming exercise, presented on Programming Praxis . The problem is easy to describe: “A mathematician purchased four items in a grocery store. He noticed that when he added the prices of the four items, the sum came to \$7.11, and when he multiplied the prices of the four items, the product came to \$7.11.” Ok, the problem is easy to get on a brute force approach. Just try all the combinations, see their sum and multiplication, and find the one that gets it. Well, easy,… Read More