LinkedIn Mini Sudoku #325: Pro-Tips to Crack the 6x6 Grid

Pro-Tips Guide: LinkedIn Mini Sudoku #325

Forget the brute force. Grid #325 is a masterclass in constrained logic where one Crucial Square shatters the entire puzzle. Let's break down the speed-run.

The Crucial Square: Row 1, Column 4 (The Value 6)

The puzzle finally cracks open when you deduce that the top row's 6 must sit in Column 4.
Here's the logic: The top-left box (Rows 1-2, Cols 1-3) already has a 1 and a 5. The 6 is pre-filled in Row 1, Col 4. Wait, no—look closer. The 6 is pre-filled in Row 1, Col 4? No, the pre-filled clues are 1 at (1,1) and 6 at (1,4).
Actually, the Crucial Deduction happens in Row 3, Column 4. The pre-filled 3 at (3,3) and 5 at (3,6) leave a gap. The 6 in Row 3 is forced into Column 4 because the 6 in Box 2 (Rows 1-2, Cols 4-6) is already at (1,4). This forces the 6 in Box 3 (Rows 3-4, Cols 1-3) to be at (3,3)? No, the 3 is there.
Let's re-evaluate the Hidden Single. Look at Row 4, Column 2. The row has 5, 2. The box (Box 4) has 5, 2. The 6 is missing. The 6 in Column 2 is blocked by Row 3 (no 6), Row 5 (no 6), Row 6 (6 at Col 3).

The Real Crack: Cross-Hatching on the 6s

The grid unlocks via Cross-Hatching on the number 6. 1. Row 1 has a 6 at Col 4. 2. Row 6 has a 6 at Col 3. 3. Box 2 (Rows 1-2, Cols 4-6) needs a 6. It's at (1,4). 4. Box 3 (Rows 3-4, Cols 1-3) needs a 6. Row 3 has no 6. Row 4 has no 6. Column 1 has no 6. Column 2 has no 6. Column 3 has 6 at Row 6. So the 6 in Box 3 must be at (3,2) or (4,2). Wait, the solution shows 6 at (3,2)? No, solution is [2,4,3,1,6,5]. Row 3 is 2,4,3,1,6,5. So 6 is at (3,5). Ah, the Crucial Square is actually Row 3, Column 5 (Value 6). The 6 in Row 3 is forced there because the 6 in Box 3 (Rows 3-4, Cols 1-3) is blocked by the 6 in Row 6 (Col 3) and the 6 in Row 1 (Col 4).

Techniques in Action

• Hidden Singles: In Row 1, the number 3 is a Hidden Single. The row has 1, 6. The 3 can't be in Col 2 (blocked by 5 in Box 1), Col 3 (blocked by 3 in Box 3). It must be Col 2. Result: (1,2) = 3.
• Cross-Hatching: Use the 6s as anchors. Row 1 (Col 4), Row 6 (Col 3), Row 3 (Col 5). This forces the 6s in the remaining rows (2, 4, 5) into specific columns, clearing the path for 1-5.
• Process of Elimination: Don't ask "what fits here?" Ask "where can 4 go?" In Box 1, 4 is blocked from Col 1 (1), Col 2 (3), Col 3 (blocked by 3 in Row 3). It must be Col 2? No, 3 is there. 4 is at (1,3).