This is a Python solution for Project Euler #96, to find the solution for sudokus.
The speed is modest (0.750s with pypy on Windows 7 @ i5 2.60GHz), but the code is relatively short and hopefully the idea is clear. Enjoy.
1. Find candidates for all items. If only one exists for a blank, fill it in.
2. Note down the blank with least but more than one candidates.
3. Copy the matrix and trial the candidates recursively until all blanks are filled.