help with advanced sudoku puzzles???

Question

i am doing a sudoku puzzle and i am totaly stuck, on very, very complex sudokus do you sometimes have to guess? it seems like that would go against the idea of sudoku puzzles but maybe i am wrong

Answer 1

Yes, the some of the hardest Sudoku puzzles do require a guess to complete them, but that will usually be outlined in the difficulty ratings. Most general public puzzles (even the "hard" and "difficult" ones) do not require a guess, and in those cases it would be best to recheck your solution so far. Hint: simply start over and see if you end up stuck at the exact same point. To start over, redraw the original puzzle on a separate sheet of paper.

As an example, the link below includes four "normal" difficulty level puzzles and one "level 5" puzzle which requires guessing.

Answer 2

I theory you should never have to guess. In practice sometimes it is too difficult to fill in another cell by logic alone.

When I do a Sudoku puzzle, I start by filling in the cells I am sure of in pen. Sometimes I can finish the whole puzzle that way. But if not, once I get stuck I write lightly in pencil the possible numbers each remaining cell could be. I write them small and at the bottom of the cell. Sometimes this exercise is enought to help me see something I couldn't see before and I can finish without guessing. But if even this doesn't work (and on a very difficult puzzle it may not) then it's time for an educated guess.

Here's how I make an educated guess. Notice I said guess, not guesses. Only guess for one cell. Pick one cell that has only two possible numbers it could be, where if you fill that cell in with your guess, it quickly leads to filling in a number of other cells. I write the number in pencil at the top of the cell and circle it. That's the starting point for my guess and circling it helps me remember which cell had the guess. Then I fill in the remaining cells at the top of each cell in pencil (without circling the number) until I either finish or reach a logical contradiction. If I finish, my guess was right and I fill in the remaining cells in pen and I am done. If I reach a logical contradiction I know my guess was wrong. I erase all the cells I filled in relying on my guess (only the numbers at the top of the cells, not the possible numbers it could be at the bottom). Then I erase my circled guess and change it to the only other thing it could be and then I finish the puzzle.

This is a systematic way to guess when you have to. And it works pretty well on difficult puzzles. And as I said, you only guess on one cell.

Answer 3

Just remember that each line up/down and left/right has the numbers 1-9. Each box has the numbers 1-9. And, diagonally each direction has the numbers 1-9.

Answer 4

guessing may be helpful. but don't guess randomly
guess the nearest possibility.
If this works choose mine as the best answer.

Answer 5

No u should never have to guess.