Twodoku - Rules & Guide

Tip 1: Think of overlap areas as “information bridges”

The only 3x3 overlapping palace grid (9 grids) in the game is the only bridge connecting the two boards. When you derive a number on the upper left disk and fill in that field, it immediately becomes a known clue on the lower right disk; and vice versa. You need to constantly use this bridge to "transport" problem-solving ammunition between the two boards.

Tip 2: The penetrating power of long-term repulsion

Although there is only one square in the overlapping area, the repulsive force of the numbers can penetrate along a straight line. If you fill in a number "8" in a row on the upper left board (non-overlapping area), you have to look along this line to check whether it can repel the overlapping area, thereby indirectly helping you eliminate the candidate numbers in the corner of the lower right board.

Tip 3: "Switch sides" immediately when encountering a bottleneck

Because the initial clues were deliberately scattered between the two boards by the question maker, when you stare at the board in the upper left corner for a long time but make no progress, don't give in. This usually means that you need to solve the board in the lower right corner first, and "feed back" the clues derived from the lower right corner to the upper left corner through the overlapping squares in the middle in order to break the deadlock and move forward.

Example image: observe the 3x3 grid shared by two 9x9 disks in the corner

A: No. Although they only overlap by 9 grids, these 9 grids are strictly bound. No single disk can be solved independently due to insufficient clues (sometimes even the overlapping area itself is completely empty at first). You must approach them both ways and treat them as a complete question.

A: Structurally speaking, Double Overlapping Sudoku (2 disks, 1 overlap) is like a "minimalist entry-level version" of Samurai Sudoku (5 disks, 4 overlaps). Their diagonal overlapping principles are completely consistent, so double overlapping Sudoku is very suitable for practicing and familiarizing yourself with the problem-solving thinking of multi-disk linkage exclusion.