How to Solve Logic Grid Puzzles

What a logic grid puzzle actually is.

A logic grid puzzle gives you a few categories and a handful of clues.
Three people, three pets, three drinks, that kind of thing.
Every person has exactly one pet and exactly one drink, and the clues let you work out who has what.

You may know them as logic problems, zebra puzzles, or Einstein puzzles.
They all work the same way.
Nothing is hidden and nothing is random.
Every answer is already in the clues, waiting to be squeezed out.

The grid is just your notes.

The grid is a way of writing down what you know.
One category runs along the top and another down the side.
Each cell is one possible pairing, like "Anna owns the cat".

You use two marks.
A cross means "impossible".
A circle means "confirmed".
That's the whole notation.

Six steps, in this order.

1. Read every clue once before you mark anything.
   Some clues only make sense together.
2. Direct clues first.
   "Ben owns the parrot" is a circle. Place it, then cross out the rest of Ben's row and the rest of the parrot's column, because a person has one pet and a pet has one owner.
3. Negative clues next.
   "Anna does not own the cat" is a cross. It looks weak, but crosses are what make elimination work.
4. Eliminate.
   A row with only one cell left uncrossed is solved. Circle it, then cross out its column.
5. Cross-reference.
   A clue that links two categories you've already connected hands you a third fact for free. "The dog owner drinks tea" plus "Anna owns the dog" means Anna drinks tea.
6. Re-read the clues after every new mark.
   A clue that gave you nothing five minutes ago may now give you everything.

Three friends, three pets, three clues.

Anna, Ben and Carla each own one of a cat, a dog and a parrot.

• Anna does not own the cat.
• Ben owns the parrot.
• Carla is allergic to dogs.

Clue 2 is direct.
Circle Ben and parrot.
Ben can't own anything else, and nobody else can own the parrot, so cross those out.

Clue 3 is a cross at Carla and dog.
Now look at Carla's row.
Parrot is crossed, dog is crossed, so Carla owns the cat.
Circle it, and cross out the cat for Anna.

Anna's row has one cell left.
Anna owns the dog.
Clue 1 said she doesn't own the cat, and indeed she doesn't.
Solved, without a single guess.

Five habits that sink most solvers.

• Guessing.
  A guess that happens to work teaches you nothing, and a guess that doesn't costs you the whole grid.
• Forgetting the crosses after a circle.
  Every circle should be followed by crossing out its row and its column. Skip it and the eliminations never come.
• Reading "next to" as "left of".
  Next to means either side. Left of means one side only. Puzzle writers love this one.
• Treating negative clues as useless.
  Crosses are the engine. Most puzzles are solved by what can't be true.
• Reading each clue once.
  Go back through the list every time the grid changes.

The same skill, with numbers.

Eitanium is this exact skill with numbers instead of names.
The 5×5 grid is the board, anchor clues are your direct clues, and direction clues are your "next to" clues.
The row totals add a way to check yourself that paper puzzles never had.

If the example above made sense, you'll be at home in the game within one level.

Try it with numbers.

Eitanium is free on Google Play.
Level 1 is gentle on purpose.