# Hitori Light

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Let's see... if I shaded in that 4, I'd have to circle the 2 next to it, which would in turn mean I'd have to shade the other 2 next to that. That's a no-no because it and the 4 would isolate the circled 2, so the 4 must be circled. Circling that 4 means the 4 down there has to be shaded, so I'll circle the... phew, I'd better take a break. The latest Conceptis Light puzzle suite, Hitori Light, certainly is a mind-bender.

In it, you're presented with a square grid of seemingly random digits ranging from 1 to the grid's size, many repeating throughout. Your job is to shade or circle every square in the grid according to three important rules. Click on squares to cycle them between circled, shaded, and undecided. What are the three rules? I'm glad you asked...

• One: no two circled squares with matching digits may exist in the same row or column.
• Two: no two shaded squares may be directly adjacent to one another (touching corners doesn't count).
• And three: no circled square or group thereof may be completely isolated from the rest by shaded squares (again, touching corners doesn't count).

It takes a very particular kind of mind to come up with the genius puzzles given such a seemingly arbitrary set of rules, a kind of mind many just don't have (*achoo!*), but there must be at least half a dozen such minds working at Conceptis to come up with a whopping 30 puzzles across three grid sizes, to say nothing of their previous Light projects like Nurikabe Light and Sym-a-Pix Light. Each puzzle is fairly entertaining and has its own unique solution, and it's easy to start formulating strategies based on specific patterns of numbers that turn up often (for example, what does it mean when you see three of a number consecutively in a row or column?).

Looking for a mind-bending distraction for a few minutes of your time? Then come shade and circle some squares. I know I am.

Play Hitori Light

### Walkthrough Guide

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Hitori Tips & Strategies

(Note: Rules One, Two, and Three are as numbered in the review.)
Common Formations and What They Mean

• The Double: If two identically numbered squares are directly adjacent, one is circled and one is shaded. This is because having both circled would violate Rule One, and having both shaded would violate Rule Two.

• The Sandwich: If a square is sandwiched between two other squares that are identically numbered to one another (but not necessarily the one in between) along a row or column, the square in the middle is circled. This is because by Rule One, one or both of the outer squares must be shaded, and no matter how this is done, Rule Two would force the middle square to be circled.

• The Double-Single: If there are three identically numbered squares in a row or column (not necessarily adjacent), and two of them form The Double, the third is definitely shaded. This is because we know from its logic above that one of the two squares in The Double is circled, and no matter which it is, Rule One applies.

• The Triple: If three identically numbered squares appear consecutively in a row or column, the one in the middle is circled, and the other two are shaded. Reapplying the logic behind The Double-Single and/or The Sandwich should make it quickly apparent why.

• The Corner: If one square in The Double is in a corner or otherwise has only one other non-shaded square adjacent to it, that other adjacent square (the one NOT part of The Double) is definitely circled. Why? If it were shaded, Rule Two would force the cornered square to be circled, and then Rule One would force the remaining square to be shaded. This would leave the cornered square completely trapped by shaded squares, violating Rule Three.

• The Gate: If The Sandwich occurs with no other unshaded squares adjacent to the middle square, exactly one of the outer squares must be circled AND the middle square may be treated as shaded when evaluating Rule Three. These are because Rule One dictates that one of the squares must be shaded, and either would put a lid on the bottleneck; also, having both shaded traps the known-to-be-circled middle square, violating Rule Three.

• Every puzzle has exactly one solution, no more, no less. Never forget that.

• Start a puzzle by looking for the formations in the above spoiler, namely The Sandwich, The Double-Single, The Triple, and The Corner. Use the information gleamed from those to start deducing other squares.

• When you shade a square, you may immediately circle all the squares adjacent to it, because of Rule Two. Likewise, when you circle a square, you may immediately shade any squares that would violate Rule One if also circled.

• Keep an eye out for "bottlenecks", narrow pathways of non-shaded squares that connect otherwise isolated parts of the grid. If blocking a bottleneck with a shaded square causes a Rule Three violation, you know where to place your circles. Remember the clause about evaluating Rule Three on The Gate.

• When in doubt, think a few steps ahead. Leave your cursor over a critical-looking square and ask, "What would it imply if I shaded this square?" ("What would it imply if I circled this square?" is typically less useful, mainly because there are two rules by which shaded squares can force circled squares and only one rule vice-versa.)

• When REALLY in doubt, take a break and go play something else. If a casual game is getting you wound up, you're doing it backwards.

I'm on puzzle #2 at the beginning and I think there are multiple correct answers. I think you can black out either of the 2's on the left column.

I hope this isn't a theme throughout the rest of the puzzles.

Ahh, I understand now. I missed the rule that all white squares must be connected.

June 14, 2012 1:53 PM

pretty easy once you get the hang of it. Couple of things to look for:

Look for 3 of the same number in a row. For every set of 3, you can shade the end numbers and circle the middle.

remember that all of the circles have to be contiguous, so you can't ever have shaded cells connecting in such a way that one or more cells are separated from the others. This makes chosing between duplicates pretty simple.

Ah, Hitori. I keep trying to learn it, but I can never quite catch on to its logic. I can get to a certain point using the really basic techniques like Neo listed, but then I get stuck because all my white areas are still open on multiple sides and I don't know what the next move is.

@ Isi

Something I do to kick me off apart from what neo said

I go across the rows circling any number that is not duplicated, then go down the columns removing any duplicate numbers

logic games are funny for me, do not think to hard and go with instinct, weird, but it works... remember also, no solid blocks next to each other - diagonal is fine, and all circles have to join overall ... but diagonals do not count as joining

I like logic puzzles. Playing a new one is always fun. I used the same basic strategy as yaddab had suggested and managed to finish most of the 5x5 puzzles in about a minute to a minute and a half. One thing I would like to see added is the ability to "lock" a square when you know it to be correct,

like in the spoiler that neo1973 indicated.

Thanks Sonic for explaining the corner - it's the tactic I've never understood until now!

June 15, 2012 6:53 AM

I'm confused about one of the puzzles.

I thought if there were two identical numbers in a row and one of them was shaded then then other could assume to be circled.

But in the 8x8 puzzles, number 3 seems to have an error unless I've misunderstood.

In this puzzle, the second column from the right has two sixes, and the solution has them both shaded. How does that work?

clickety6:
There can't be two of the same number circled in a row, but there can be many of the same number shaded in the same row.

June 15, 2012 8:19 AM

I understood that only one number of a type could be circled, but up until that puzzle, if I had two 6's and one of them was shaded, I had assumed the other 6 would be circled, not that both could be shaded. Same as if I saw a single number that wasn't repeated in a row or column, I assumed it would be circled - but maybe that as a bad assumption too?

clickety6

I have found it to be true SO FAR that if there is only one number in a row and column then it would be circled. That has been my start point for the ones I have completed so far

June 16, 2012 6:31 PM

Here are some advanced strategies that haven't been mentioned before:

"The snake:"
With a long chain of shades, suppose there are two breaks: if for one, it is separated by two identical numbers, then if the other break forms a closure, it must be circled.
eg:
| 0 0 0 0 0 |
| V 0 8 0 P |
| 0 V 0 V 0 |
| 0 0 8 0 P |
| 0 0 0 0 0 |
Where V = shaded, 0 = other cell, P = cells that must be circled by this rule.
The snake can theoretically extend to any number of breaks.

"The gamble:"
When no common pattern applies and you wish not to enter recursive induction, sometimes you can spot a case in which one of the pair of numbers is completely surrounded already. In this case, shade it. More generally, shade a member of a multiple if you conclude (logically) that it CANNOT FORM ANY ISLANDS, OR if all the other members, if shaded, can form the same islands, plus more. In this case, we can shade the suspect cell.
It's called a gamble because if you don't use the "isolation" reasoning correctly, you're just guessing.

The above are not as common as patterns, but I've used each more than 10 times throughout the entire game, mostly when the only alternative was recursion.

June 17, 2012 5:20 PM

@clickety6: The solution to the third 8x8 puzzle is correct.

Both 6's in the second column from the right are shaded because there are other 6's in each of their rows. AFAIK your strategy of circling a number if it is not duplicated is correct, provided you take into account both the column AND the row it is in.

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