🚀 Getting Started: how to approach Sudoku
Sudoku is a logic puzzle — you do not calculate, you eliminate possibilities. The key is candidate notation (small pencil marks) and a consistent solving cycle. 🧠
📝 1) Write down candidates
In each empty cell, note the possible digits from 1–9 that fit the row, column, and 3×3 box. Then update nearby candidates after every placement.
🔁 2) Work in cycles
singles → update candidates → patterns → repeat. Most dead ends happen only when you stop cleaning up candidates.
Pro tip: if you get stuck, go back to Hidden Singles and blocking techniques. These are the moves that most often unlock medium Sudoku puzzles. 🔓
1️⃣ Naked Single — a single remaining candidate
When it works: when only one digit remains in a cell after elimination. What you do: place it and remove it from candidates in the same row, column, and box. ✍️
🎯 Quick tip
First, look for cells with the fewest candidates. They often create a chain of new forced moves.
2️⃣ Hidden Single — the only place in an area
When it works: in a row, column, or box, a digit can go into only one cell — even if that cell still has multiple candidates. 🔎
🧩 How to spot it
Pick one digit (for example, 9) and scan the area: where can it go? If only one cell remains, place it.
3️⃣ Naked Pairs / Triples — exposed pairs (and triples)
When it works: in a row, column, or box, two cells contain the same pair of candidates (for example, {2,8}). Those digits must go there, so you can remove them from the rest of the area. 🧹
👀 Where are they easiest to spot?
Start with 3×3 boxes. Then check rows and columns.
4️⃣ Blocking — Pointing Pairs & Box-Line Reduction
This is one of the most rewarding techniques at the intermediate level. It connects a 3×3 box with a line (row or column). 🔥
📌 Pointing Pair
If all possible positions for a digit inside a box are in the same row (or column), you can remove that digit from the rest of that row (or column) outside the box.
🧱 Box-Line Reduction
If, in a row, a digit can only appear inside one specific box, remove that digit from the other cells of that box.
5️⃣ X-Wing — a rectangle that breaks a stalemate
When it works: for a given digit (for example, 5), you find two rows where that digit appears as a candidate in exactly the same two columns. This creates a rectangle, and then you can remove that digit from other cells in those columns outside the X-Wing rows. ✂️
🎛️ How to find it quickly
Choose one digit and scan the rows: where does it have exactly two candidate positions? You are looking for a repeated column pattern.
✅ Checklist: what to do when you get stuck
Tick these off (saved locally). In practice, this is a reliable Sudoku unblocking routine. 🧠