Straight Sudoku
(Published in Czech Republic Academic Championship)
Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each row, column and 3x3 box. Moreover, the indicated lines in the grid should contain straight consecutive digits (e.g. 1-2-3-4, not 1-2-3-2!). Where there is no indicated line there can't be any straight horizontal, vertical or diagonal line which contains more than 2 consecutive numbers.
