What are some concrete tips for solving nonograms (paint-by-numbers puzzles, like the ones in _Games_ magazine)?

Here are a few keys:

- When you're just starting out, here's how you find out if a row will
generate squares.  Add all of the numbers in the row together, and then
add one for each blank space between the numbers.  Then add in the largest
number -- if this is more than the number of squares in the row, then
you'll be able to fill in some black squares.  EXAMPLE: If the row is "6 3
3 7" and there are 25 squares in the row, then you know that this is good
because 6+3+3+7+3+7>25.  A corollary of this is that a single number will
generate squares if it is more than half of the number of squares in the
row, obviously.

- Pay more attention to the edges than to the center of the diagram.  If
you completely solved one of the edge rows, then you'll be able to get
lots of useful information in the opposite dimension.

- Another edge trick is to look to see if there are situations where the
edge row is like "8" and the row next to it is like "2 2".  This means
that most of the edge row has to go where there are "1"'s in the opposite
direction.

If you can find Games Magazine's "Paint By Numbers" book, it has a good
step-by-step solution to a 15x15 puzzle that talks about every picayune
strategy.  Plus 123 more puzzles.

>Out of curiosity, does anyone know concrete
>criteria for a soluble paint-by-numbers puzzle?

Not I.  I think that most of them are solvable, it's just that you don't
know how hard they are to solve until you actually do it.

-- Matthew Daly <mwdaly@pobox.com>, January 1998
   (question posted by Christina <s773461@UOTTAWA.CA>)