This popular Japanese number puzzle has just one easy rule: In every Row, every Column and every 3x3 sub-grid, all the numbers from 1 to 9 should appear, but only once in each row, column and sub-grid.
+------+-------+------+
| 0 0 0 | 7 0 0 | 4 0 0 |
| 0 3 0 | 0 9 0 | 0 2 0 |
| 4 0 0 | 0 0 5 | 0 0 0 |
+------+-------+------+
| 0 0 8 | 0 0 0 | 0 0 5 |
| 0 9 0 | 0 3 0 | 0 7 0 |
| 6 0 0 | 0 0 0 | 3 0 0 |
+------+-------+------+
| 0 0 0 | 4 0 0 | 0 0 6 |
| 0 7 0 | 0 2 0 | 0 9 0 |
| 0 0 5 | 0 0 8 | 0 0 0 |
+------+-------+------+

Replace the 0's with the digits required to satisfy the rule.

(In reply to again... by pcbouhid)

In addition to pcbouhid's two, I place a 7 in the bottom right corner of the fourth square (first on second row), and a 3 in the top right corner of the seventh square (first on third row). The latter is a bit harder to see why; it's because the only places that 4 and 6 can go in that square are above and to the left of the 5, so one of the two numbers must go in each spot. So the only space left for the 3 has to be the top right corner.

Posted by Avin on 2005-05-13 21:03:43