Also the rules of hitori say that a number cannot appear more than once.
So can we use the reverse rule : Circling a particular number (or shading in yellow as in above case) if its another occurence in the same row/column has been shaded (in grey color as in above) because this ensures that the number will always occur once (and cannot appear 'zero' times) ?

I dont know if i've been clear with the description of my doubts !
so yeah..thanks anyway :)

Hi Sanket,

1. If a number occurs exactly once in the row 'and' column corresponding to the cell, that number has to be circled for the solution to be unique (which is what you have done). But this is unlikely to help you solve the puzzle as it does not help you 'progress' in any way, it only helps in 'completing' the puzzle.
2. In the above puzzle, I think your starting point should be the top-left corner. If you shade R2C1, then R1C2 will be shaded forming a contradiction. Hence R2C1 is circled.

Edited by Rohan Rao 2011-05-07 10:29 PM

hmm..
yeah i started in the same manner as you mentioned...
and what about the reversal rule?
thanks anyway :)

The reversal rule is true because if you find a solution where an unique (yellow) number is black then you can change this black square to yellow. And you will have another correct solution. So there is a solution where every unique number is yellow. And if the puzzle is correct this is the unique solution.

If a number appears only once in a row/column is it necessary to circle it?????and if a number appears more than once in a row/column is it necessary to circle one of them??????

Not necessarily. Try this:
1112
2341
1213
2421

Observe C3. Both of its 1s are shaded, leaving no 1 remaining.

To above: The first is yes if the solution is guaranteed to be unique (but no otherwise), the second is no.