Brainless Sudoku

[prog]

Puzzle people:

Is this for real? Can all Sudoku be solved - and solved relatively quickly - by this brute force method?

If so, I think that's pretty funny.

Comments

[grr-plus1.livejournal.com]

This is an OK strategy for easy and moderate Sudokus (although writing in all 9 numbers in each small square and erasing them is far more laborious than necessary). It is _not_ a way to solve all Sudokus. It would probably fail on a good proportion of, say, the Sunday Globe Sudokus.

Some particularly tough ones require extra tricks. For instance you may have 5 squares in a box/column/row showing these possibilities: [12345][235][123][13][123]. This looks intractable using the "brainless sudoku" method. However, the last 3 boxes have only 3 numbers to split between them, and must be filled in with 1,2 & 3 in some combination. Even though you may not yet know what this combination is, you can still eliminate 1,2&3 from the 1st 2 boxes, allowing you to solve them as 4 & 5, respectively. This scales for any number of boxes. I just encountered one puzzle in which the "brainless" method failed to specify ANY numbers, and I required multiple applications of this trick to get anywhere.

Then there are the _really_ hard ones that linear brute-force methods come to a complete dead end for. These ones you have to make a guess (usually between 2 possible numbers for a box) and see how it plays out. If it leads to an inconsistency, you then have to backtrack & test the other number instead. Extremely nasty Sudokus may force you to test multiple branchings before you find the correct combination.