Let's enter the toughest known SuDoku puzzle and see if we can solve it. Just drag and drop the red numbers to the puzzle cells. If you make a mistake just double-click on the number and it disappears. When finished, "Save" the puzzle and you're ready to Solve it.

Here it is, ready to go, we saved it as "toughestknownpuzzle.txt". Shall we try to Solve it ourselves, or will we admit defeat and give it to NINJA's mighty "Auto Solve" feature?

We'll try to solve it manually. NINJA gives us all the tools. First of all, notice at this point in the "Moves" section at Row 2, Col 6 only the 4 can be played. And at 3,9 only the 6 can be played. When you Drag and Drop the numbers onto the board the moves are recorded and placed in the "History" section so you never lose a move. But we don't even have to Drag and Drop--we simply click on the buttons on the bottom and NINJA does it for us! Notice the checked moves in the "History" section, these are "decision points" where you had previously picked one of two possible moves. If that path doesn't work out you can go back to that point and pick the other one and continue.

Whoops! we almost thought we had it! We hit another dead end and now we have to  back up to the last "decision point" and take the other path...no problem with our NINJA...

Well, it turns out this really was a tough one! It's probably impossible to be solved by a human being. We gave up and turned it over to NINJA's famous "Auto Solve," which took only 6.9 seconds. (That's actually a long time; most sols take less than a second.) Notice that the "Moves" section is empty and the "History" section is filled up. You can click on the lower right button and delete--or replace--the last move(s) and they will be erased from the board and put back in the "Moves" section, all the way to the beginning. You can Save your puzzle at any time and/or Print it out with its entire move history for future reference. Why try to work another SuDoku puzzle without it! Get your NINJA today!