LinkedIn 6x6 Sudoku #337: The Crucial Square That Cracked the Grid

Pro-Tips for LinkedIn 6x6 Sudoku #337

This grid is a speed-run trap: it looks open but hides a crucial square that unlocks the entire solve. Don’t hunt randomly. Start with the densest units and let forced moves do the work.

1. Start with the Fullest Houses

Rows 2 and 3 each have 4 givens. Columns 2 and 4 have 4 givens. These are your fastest exclusions. In a 6x6, rows with 4+ numbers often reveal naked singles immediately.

2. Cross-Hatching in Action

Pick a missing digit like 2. Scan row 3 (which needs a 2). Then scan column 6 (which also needs a 2). The overlap is row 3, column 6. Cross-hatch the block (rows 3-4, cols 4-6): the 2 in row 2, column 4 blocks column 4. The 2 in row 4, column 6 blocks column 6. Only row 3, column 6 survives. Drop the 2 there. Boom, row 3 gains traction.

3. The Crucial Square: R3C5

After placing the 2 in R3C6, row 3 has givens 2, 5, _, _, 4, 2 (wait, no, row 3 is 2, 5, _, _, 4, _). The missing digits are 1, 3, 6. Now scan box 2 (rows 1-2, cols 4-6): 1 is already in row 2, column 4. Row 1, column 4 is 1. So 1 in row 3 must go to column 5. R3C5 is a hidden single for 1. This is the crucial square. Place it and the grid cracks open.

4. Chain the Cascade

With 1 in R3C5, row 3 now needs 3, 6. Column 5 has 1, 4, 2, 5 (from given and solved). Only 3 and 6 fit. Column 4 has 1, 2, 5. Only 3 fits in R3C4. Drop 3 in R3C4, then 6 in R3C3. Row 3 is full. Now column 3 has 2, 5, 6, 4. Only 1 and 3 remain. Row 5, column 3 is 4 (given), so 1 and 3 go to R1C3 and R6C3. But row 1 already has 1 in column 4. So R1C3 = 3, R6C3 = 1. The cascade ripples to column 1 and 2.

5. Hidden Singles Finish the Job

After the cascade, box 3 (rows 3-4, cols 1-3) is nearly full. Only 6 and 3 remain. Row 4, column 1 has no 6 or 3. But column 1 has 1, 2, 6 (from given and solved). So 3 must go to R4C1. Hidden single for 3. Then 6 goes to R4C3. The rest are naked singles.

Final Answer Path

Start densest units → cross-hatch 2 into R3C6 → spot hidden single 1 at R3C5 (crucial square) → cascade 3 and 6 in row 3 → chain to column 3 → finish with hidden/naked singles. The whole grid flows from that one square.

Key Takeaways for #337

• Cross-hatching eliminates candidates by slashing rows/columns where a digit blocks.
• Hidden singles are digits with only one legal spot in a box or row.
• Crucial square R3C5 (the 1) is the unlock. Without it, the grid stalls.
• Trust forced moves over pretty chains. Scan, place, rescan.