Masyu
Rules
Draw a single closed loop which runs horizontally or vertically between the centers of the cells. The loop cannot intersect or touch itself. The loop must visit all cells with circles. In a cell with a black circle the loop must turn by 90° and must travel straight through the previous and next cell. In a cell with a white circle the loop must travel straight through and must turn by 90° on the previous or the next cell.
Click to see the answer.