Difficult Sudoku
Dunno why, but feel that this puzzle is very difficult. Took a long time to get the answer.
The rules are simple, just ensure all vertical and horizontal lines contain the number from 1 to 9, as well as each 3x3 small boxes in bold contained 1 to 9 too.
Dun need to do by trial and error one, each boxes can be derived through logic and there are no ambiguity, there can only be one correct answer.
