Masyu

Description
Masyu is a loop-drawing logic puzzle where a single, non-intersecting loop that passes through all circled cells is drawn.

Rules
The objective is to draw a single, non-intersecting loop, subject to the following rules:
 * 1) All circles must be passed through exactly once.
 * 2) At black cells the loop has a turn of 90°. The loop must also go straight through the cells immediately before and after on the path.
 * 3) At white cells the line travels straight through. The must turn in the cells immediately before and/or after on the path.

Example
A standard 10x10 masyu and its solution.



Variants
Unless otherwise indicated, standard masyu rules apply to all variants.

Grey Cirles: In addition to black and white cirlces, grey circles appear which can act as either colour.

Regional: The grid is divided up into regions. The loop must turn an equal number of times in each region.