Challenging Logic Puzzles: Irupu Puzzles - 100 Logic Grid Puzzles With Answers

("I-Loop") is a logic puzzle invented by Naoki Inaba (Japan). A rectangular or square grid contains circles in some cells. The goal is to locate some blocks in the grid, having the size either 1 x 3 or 3 x 1. Each block contains one circle and must be orthogonally adjacent to exactly two other blocks. All block cells form one contiguous region.