I started to embed logical techniques into the generator in JSudoku.
Not yet fully implemented, but here are the very first results. Comments & suggestions are welcome.
Hard (requires X-Wing, but no harder technique)
Code:
5137...........7.5.6.5....2....3.86.2.7..6.......9..7.4....2........9.....5......
..8..1...7...38.........41..9..2...42.6.....9.3.68..........9.....293.........86.
...6........9........3.........2..14..2...5..16..9.........9........4........5...
.23.........837.....9..........49.5.9.....3.71...6..2..34.........41...9...2..8..
......7.....4........7....5.8..3.......8..9.4.31.6....8....9.5.3.2...........1248
Very easy (solves with hidden singles only, several possible singles at each step)
The idea is: it could be solved without pencil marks.
Code:
.97..1........7.835....9.2...67..5.2..2.6..4.....8.1.773........5.1.8...6..3.....
...6..38.68.5......4.8....75.3..61...1..3.6..8.2.5...........96...7.8.3......9..2
.....................2.3....21...87....8.9....83...49....1.6.....................
6..4......2.1.7...78...........4.6.5..9.6..4...65..9.11....5.7......4.93.47..9...
.....6..5...2.8.6........147.3.8.....2..9.5..8.4..39...6.9....727.5........8..25.