Hard boards are 8x8, and the hints from the beginner and Normal guides only take you part of the way. At some point you have to look at two or three colors at once. Let's solve Hard 519 together. The first eight moves are a warm-up with hints you already know. The new ideas come at moves 9, 10 and 11.
PetDoku is a Queens puzzle. It has the same rules as Queens puzzles (including the daily Queens game on LinkedIn), Meowdoku and other cat sudoku and animal sudoku apps, so you can use everything in this guide in PetDoku, Queens puzzles and Meowdoku alike.
Hard 519. Eight colors, eight pets.
Start: the one-square color
The lime square on the right edge is a color on its own. Place its pet and clear its row, column and neighbors.
Warm-up: squeezed colors and touched squares (moves 2-8)
2. Both red squares are in the top row, so the rest of that row is X.3. Both purple choices are in the seventh column, so the rest of that column is X.4. Both choices in the top row touch the two orange squares below them.5. Both choices in the seventh column touch the two blue squares to their left.6. Orange is down to two choices, and both touch the same three squares.7. The top row has one square left.8. Teal has two choices, one in the same column and one in the same row as a yellow square. That square is X.
Nothing new so far, but look at how much of the board these simple hints cleared. On Hard boards it pays to run through them again after every few moves. Now the board stops giving easy moves.
Hint 1: Two columns that fit inside two colors
Every choice left in the fifth and sixth columns is yellow or blue. Those two columns need two pets, and only yellow and blue can give them. So yellow and blue are both used up here, and their squares outside these columns are X.
This is the Normal guide's two-color hint turned around. There, two colors fit inside two lines. Here, two lines fit inside two colors. Either way, the pets are spoken for: two lines, two colors, two pets. Everything of those colors outside the lines can go.
Hint 2: Three colors that share three rows
Orange, yellow and teal only have choices in the second, third and fifth rows. Three colors need three pets, and those three pets fill all three rows. The blue squares in those rows are X.
The same idea with three. It is harder to spot because you need to hold three colors in your head. A good way to search is to start from the colors with the fewest choices left, write down which rows they reach, and add one more color at a time. When the number of rows equals the number of colors, you have a lock.
Hint 3: Try a square and see what breaks
The fifth and sixth columns belong to yellow and blue (Hint 1). Suppose the yellow pet went on the red X square. The sixth column would then need the blue pet, but its only blue square touches the red X square diagonally. The sixth column would have nowhere left, so the red X square is out.
Once you know two lines belong to two colors, you can test a square in your head: put a pet there and see whether the other line still has room. If it does not, the square is X. (The upper square in the sixth column does not help here, because it is yellow and yellow would already be used.)
Finish: one empty square at a time
12. The fifth row has one square left.13. Then the third row.14. Then the second row.15. The bottom row has one left.16. Then the seventh row.17. The last pet goes in the sixth row.
Solved: eight pets, one in each color, row and column.
How to look for locks on Hard boards
Run through the simple hints first. They clear more than you expect.
Sort the colors by how many choices they have left. Locks usually hide among the smallest ones.
For two or three colors, list the rows (or columns) they reach. Same count of colors and lines means a lock.
Try it the other way too: two or three lines whose choices fit inside the same number of colors.
After finding a lock, try a pet on a square in one line and check that the other line still has room.
PetDoku The JoyPlus Soft Planning Team
