Rules: Draw a single, non-intersecting loop running through the cells’ centers. The loop may not run diagonally: only up, down, left, and right. The loop must visit all the pearls: additionally, the pearls constrain how the loop moves through them. On a white pearl, the loop must go straight through, and it must make a turn directly before or after the pearl (or both). On a black pearl, the loop must make a turn, and it may not turn right before nor right after the pearl.
This puzzle type was invented by Nikoli.