CIS 554 Sudoku puzzles
Fall 2012, David Matuszek

The following are probably solvable by your program (I haven't tested them).

  _ 8 _   _ _ _   2 _ 5 
  7 _ 1   4 _ _   _ 8 9
  9 _ _   3 5 _   _ 1 _
          
  _ _ 9   _ _ 7   6 3 _
  _ _ 2   _ _ 9   7 _ _
  _ 7 8   5 _ _   _ _ _
          
  _ 6 _   _ 4 5   _ _ 3
  2 9 _   _ _ 6   5 _ 1
  4 _ 5   _ _ _   8 7 _
  _ 1 6   _ _ 9   _ _ 2 
  _ _ _   _ 3 1   _ 4 _
  8 7 _   5 2 _   _ 1 _

  _ _ 9   _ 8 _   2 _ 1
  5 _ _   6 _ 7   _ _ 9
  4 _ 1   _ 5 _   3 _ _

  _ 4 _   _ 7 8   _ 9 5
  _ 9 _   3 6 _   _ _ _
  2 _ _   1 _ _   6 3 _
  _ _ 4   _ _ _   _ 6 7
  3 _ _   4 7 _   _ _ 5
  1 5 _   8 2 _   _ _ 3


  _ _ 6   _ _ _   _ 3 1
  8 _ 2   1 _ 5   6 _ 4
  4 1 _   _ _ _   9 _ _


  7 _ _   _ 8 _   _ 4 6
  6 _ _   _ 1 2   _ _ _
  9 3 _   _ _ _   7 1 _
  _ _ _   2 _ 3   9 6 _
  2 _ 6   _ _ 7   _ 3 _
  7 _ _   1 5 _   8 _ _


  3 6 _   _ 7 2   5 _ 1
  _ _ _   _ _ _   _ _ _
  4 _ 8   6 _ _   3 7 9


  _ _ 7   _ 6 8   _ _ 3
  _ 3 _   7 _ _   4 _ 6
  _ 1 2   9 _ 4   _ _ _

The following are probably not completely solvable by your program.

  _ _ _   9 7 _   5 _ _ 
  3 _ 1   _ _ 4   _ _ 9
  _ 7 _   _ _ 2   1 _ 8
          
  7 _ _   2 _ _   _ _ 6
  _ _ 9   _ _ _   4 _ _
  8 _ _   _ _ 3   _ _ 7
          
  6 _ 3   1 _ _   _ 2 _
  4 _ _   5 _ _   8 _ 1
  _ _ 7   _ 2 8   _ _ _
  _ _ 6   _ _ 3   _ _ _ 
  1 _ _   8 _ _   4 6 _
  _ 4 _   5 _ 6   9 _ _

  _ _ _   4 _ _   2 9 _
  _ _ 4   1 _ 5   3 _ _
  _ 6 9   _ _ 8   _ _ _

  _ _ 8   6 _ 4   _ 3 _
  _ 2 5   _ _ 1   _ _ 9
  _ _ _   9 _ _   7 _ _

The assignment says:

The format should be nine lines, with nine numbers on a line, separated by whitespace (spaces and/or tabs). For extra neatness, allow blank lines in the input. Use underscore, _, to indicated a "blank" (unfilled) location in the puzzle.

It is not difficult to skip over whitespace and blank lines. Please allow arbitrary whitespace in an around lines, and allow blank lines. This is easy enough to do that you should not burden the user with knowing your unnecessarily exact requirements.