Masyu

Rules: Draw a single closed loop which travels between orthogonally adjacent cells, visits every clue cell, and does not visit any cell more than once. For every white circle, the loop must go straight through it and turn either immediately before or immediately after it (or both). For every black circle, the loop must turn at it and go straight both immediately before and immediately after it.

Example:

m-0

[Solution]

Here is the Wikipedia article.