This is a Graffiti snake puzzle.
Paint some cells black to form a wall. The numbers outside the grid indicate the number of blackened cells in the corresponding direction, in order, as in a Paint by Number puzzle. If there is more than one blackened block in a row or column there has to be a white cell between the blocks. Additionally, a snake must pass through all the remaining white cells, moving horizontally and vertically and not touching itself, not even diagonally. The head and tail of the snake are given as the grey circles.
I referred to the IB of Puzzle Marathon for rules. You can see that IB by clicking here.
Rating : Hard? For the blog definitely. I don’t really know about LMI test related ratings for this one.
Solution and a bit of a tip added(Well, quite a basic one, but I found that many people don’t know it) : Click here. Password : GS.