Guides › Puzzles
A Beginner's Method for Logic Puzzles: Sudoku, Queens and Light Switches
By the Nerdania team · · 4 min read
Logic puzzles can look intimidating: a grid of numbers, a board of switches, an empty chessboard. But nearly every logic puzzle can be solved with the same handful of ideas. Once you learn them, puzzles like Sudoku Sanctum, Queens Court, Lumen Lock and Bridge Ledger stop being guessing games and become satisfying chains of small, certain steps.
The golden rule: never guess when you can deduce
A well-made logic puzzle has exactly one solution, and you can reach it without guessing. Every number you place should be placed because it must go there. If you catch yourself thinking "maybe", stop and look for a square where you can be sure. Guessing works occasionally, but it usually leads to a tangle you cannot undo.
Four ideas that solve most puzzles
1. Find the most constrained spot
Look for the place with the fewest options. In Sudoku, it is the row, column or box that is almost full. In Queens Court, it is the row where most squares are already attacked. Starting there gives you certainty quickly.
2. Use elimination
Often you cannot see what goes in a square directly, but you can rule out everything else. If a Sudoku square cannot be 1, 2, 3 or 4 because those numbers already appear in its row, column or box, and only 5 is left, it must be 5.
3. Ask "where can this go?"
Turn the question around. Instead of asking what goes in a square, ask where a particular number can go in a row or box. If the number 3 has only one possible home in a box, place it, even if that square could theoretically hold other numbers.
4. Follow the consequences
Every certain move creates new information. After placing a number or a queen, immediately check what it rules out nearby. Good solvers work in chains: one move unlocks the next.
Sudoku: getting started
Sudoku Sanctum begins with small boards using four digits, which is the best way to learn. The rule is always the same: each row, each column and each outlined box must contain every number exactly once.
- Scan one number at a time. Pick the number that appears most often on the board, and find every box where it is still missing. See if the existing copies in nearby rows and columns leave only one square.
- Check almost-full groups. A row with only one blank square is free: fill in whatever is missing.
- Take your time. In Sudoku Sanctum incorrect numbers cost a life, so it pays to be certain.
Queens: placing pieces without conflict
In Queens Court you place one queen in each row so that no two share a column or a diagonal. This is a version of the famous "eight queens" puzzle.
- Work row by row. Place a queen in the first row, then move to the next row and pick the first safe square.
- Shade the attacked squares in your mind. Every queen attacks her whole column and both diagonals.
- Back up when you are stuck. If a row has no safe squares, move the queen in the previous row to her next safe square and continue. This methodical "backtracking" always finds an answer.
- Avoid the very corners at first. Corner queens tend to block a long diagonal; starting a little in from the edge often works sooner.
Light switch puzzles
In Lumen Lock and Lights Logic Lab, tapping a light flips it and its neighbours, and your goal is to switch everything off. These puzzles have two surprising properties that make them much easier once you know them:
- Order does not matter. Tapping A then B gives the same result as tapping B then A.
- Tapping twice cancels out. Tapping the same light twice returns the board to where it was. So in any solution, each light is tapped either once or not at all.
A popular strategy is called chasing the lights. Work from the top row down: for every light that is still on in a row, tap the light directly below it. This switches off the row above without disturbing the rows you have already cleared. When you reach the bottom, only the last row may still have lights on. With practice you learn which taps in the top row clear each bottom-row pattern, then repeat the chase.
Bridges and networks
Bridge Ledger asks you to connect islands with bridges so that each island has exactly the number of bridges shown, and bridges never cross. Copper Current asks you to rotate pipe pieces into one connected network.
- Start at the edges and corners. A corner island or pipe has fewer possible connections, so its choices are forced first.
- Look for "full" numbers. An island showing 4 with only two neighbours must have two bridges to each.
- Avoid closed loops. In network puzzles, a loop that closes too early cuts off the rest of the board.
Sliding and sorting puzzles
Mosaic Vault is a classic sliding-tile puzzle, and Prism Vials is a colour-sorting puzzle. For sliding puzzles, solve the top row first, then the left column, then treat what remains as a smaller puzzle. For sorting puzzles, an empty vial is your most valuable tool – avoid filling it unless the move makes real progress.
When you are truly stuck
- Walk away briefly. Returning with fresh eyes often reveals an obvious move you missed.
- Re-check the rules. Many "impossible" boards come from a misread rule.
- Look at a different part of the board. Fixating on one hard corner wastes time when an easy deduction waits elsewhere.
Logic puzzles are among the most rewarding games because every success is earned by your own reasoning. Explore the full puzzle collection and the cards and logic games to find your favourite.