This section of the site is dedicated to my appallingly unhealthy fascination with a number game popularised by the Channel 4 (UK) gameshow, Countdown. In this game, a given contestant semi-randomly selects 6 numbers from the set...
{{1-10}, {1-10}, 25, 50, 75, 100}
...and is then supplied with a random target number (T) in the range 101-999. The challenge is to generate T (or a number as close as possible to it) using any of the numbers chosen and employing only simple arithmetic operations (+, −, × and ÷). Each number can only be used once.
This is computationally interesting as it can be framed as a classic recursive search problem. Indeed, the solver presented below works in precisely this manner.