LinkedIn Mini Sudoku #216: The Row 5 Breakthrough

The Setup

Puzzle #216 opens with a sparse grid: just 9 clues scattered across the board. The top-right corner is fully exposed (1-2-3 in Row 1, then 4-5 stacked below), and Row 5 has three anchors at positions 2, 3, and 4. At first glance, it feels manageable. Then you realize the entire left column is dark.

Initial Scan: Cross-Hatching the Extremes

Start with Column 1, the empty sleeve. It needs 1-6, and your clues are scattered:

• Row 3, Column 2 has a 4 (blocks 4 from Row 3, Column 1)
• Row 4, Column 2 has a 6 (blocks 6 from Row 4, Column 1)
• Row 5, Column 1 is given as empty, but Row 5 already shows 3-1-4 in positions 2-3-4

This is where cross-hatching becomes your best friend. For each empty cell in Column 1, ask: "What numbers are already in this row? What numbers are already in this region?" The intersection of eliminated candidates narrows your field fast.

The Crucial Square: Row 5, Column 5

This is where the puzzle cracks. Row 5 reads: [blank, 3, 1, 4, blank, blank]. It's missing 2, 5, and 6.

Now cross-hatch Column 5:

• Row 1 has 2 (blocks 2)
• Row 2 has 6 (blocks 6)
• Row 3 has 3 (blocks 3)
• Row 4 needs checking via its region and row constraints

The bottom-right region already has 1-4 from Row 5. For Row 5, Column 5 to be valid, it must avoid 1, 3, 4, and 2, 6 from its column. That leaves 5 as the only candidate. This is a hidden single—the number is forced, even though Row 5 has multiple empty cells.

Once you lock 5 into Row 5, Column 5, the domino effect cascades. Row 5 now needs only 2 and 6 in the remaining positions, and region logic tightens every adjacent cell.

Pro-Tips for #216

Technique 1: Region-First Elimination
Don't just scan rows and columns in isolation. The six 2x3 regions are your constraint multipliers. If a region already has 1, 2, 3 and 4, then the two empty cells must be 5 and 6. Use this to prune candidates in those rows and columns immediately.

Technique 2: The Empty Column Trap
Column 1 looks hopeless at first, but it's actually a goldmine. With zero given clues, every number you place elsewhere eliminates candidates for Column 1. Wait until Rows and Regions are partially solved, then sweep Column 1—each cell will have fewer options than it appeared to have initially.

Technique 3: Pairs Within Regions
Once you narrow a region to two candidates (e.g., "this region needs only 2 and 5 in cells A and B"), those two cells lock a pair. Immediately remove 2 and 5 from all other cells in their shared rows and columns. This cuts your search space by a third.

The Endgame

After Row 5 crystallizes, Rows 3 and 4 follow quickly—they share regions with the now-tighter Row 5 constraints. The top half (Rows 1-2) were nearly solved already; they just needed the column constraints to ripple down. By the time you reach Rows 5-6 with full clarity, the puzzle collapses in seconds.

Speed-run note: Don't guess. If you feel stuck, you've missed a hidden single or a region constraint. Re-scan the regions first—they're the puzzle's true backbone.