Medium Sudoku
Choose a number, and place it in the grid above.
Medium Sudoku: Elevating Your Logic
If Easy Sudoku is a "warm-up," then Medium Sudoku is a true mental workout. At this level, the number of starting hints drops (typically to 25–30 clues), and simple observation is rarely enough to complete the grid.
The beauty of Medium Sudoku lies in the concepts of "space-holding" and "interconnectedness." You can no longer look at cells in isolation; you must observe how numbers across the board restrict and influence one another.
Core Techniques for Medium Sudoku
When basic scanning hits a dead end, use these advanced logical maneuvers to break the stalemate:
1. Locked Candidates (Claiming)
This is the hallmark of a Medium-level solver. Sometimes you can’t tell exactly where a number goes within a 3 × 3 block, but you can see it must fall within a specific row or column inside that block.
The Logic: If the number 3 must appear in the top row of a specific block, then 3 cannot appear anywhere else in that same row in other blocks.
The Result: This "ghost" presence allows you to eliminate candidates in neighboring sections, clearing a path forward.
2. Naked Pairs & Triples
When you find two empty squares in the same row, column, or block that can only contain the same two numbers (e.g., 2 and 5), those two numbers have effectively "claimed" those spots.
The Logic: Even if you don't know which spot is 2 and which is 5, you know for certain that no other square in that unit can contain a 2 or a 5.
The Result: This drastically reduces the possibilities for remaining squares, often triggering a "Sole Candidate" reveal.
3. Hidden Pairs
This is the inverse of a Naked Pair. If you notice that two numbers (e.g., 7 and 8) can only possibly fit into two specific squares within a unit—even if those squares have other potential candidates—the 7 and 8 "hide" there.
The Logic: Since 7 and 8 must occupy those two spots to satisfy the rules, you can safely delete all other candidate numbers from those two squares.
Strategies for Success
Use Pencil Marks
In Medium difficulty, noting down "candidates" (tiny numbers in the corners of cells) is essential. It helps you visualize pairs and patterns that are impossible to keep track of mentally.
Scan the Intersections
Focus on where a nearly full row meets a nearly full 3 × 3 block. These intersections are often where the first "Locked Candidate" appears.
Expect the "Chain Reaction"
Medium puzzles usually have one or two "bottlenecks." Once you use logic to crack one difficult number, the rest of the puzzle often collapses into a series of easy moves.