🔧 Step-by-Step Answer Walkthrough For Easy Level
Locate the constraint that covers exactly one cell. Its sum target is 1, which means the pip placed on that cell must equal exactly 1. No other value is possible — a one-cell region with sum 1 is fully determined before you know anything else about the board.
Only one piece in the set has a 1-pip end: the 4–1 domino. It must land here, with its 1-end in the sum-1 cell at row 1, column 3, and its 4-end extending downward to row 2, column 3. No other orientation or domino can satisfy this constraint.
Two cells in column 2 — rows 0 and 1 — must show equal pips. The 3–3 double is the natural fit: both ends are identical, so the constraint is satisfied regardless of orientation. Place it vertically in column 2, rows 0–1.
The 4-end of the 4–1 domino sits at row 2, column 3. The region covering rows 2–3 in column 3 requires those two cells to be equal — so row 3, column 3 must also be 4. The 4–2 domino carries a 4: place it horizontal at row 3, columns 2–3, with 4 on the right and 2 on the left. Row 3 column 2 is now 2.
Rows 3, columns 1–2 must be equal. Row 3, column 2 = 2, so row 3, column 1 = 2 as well. The 2–0 domino runs vertically at column 1, rows 2–3: 2 at row 3, 0 at row 2. That sets column 1, row 2 = 0. The equals pair at rows 1–2, column 1 needs both cells equal: row 2, column 1 = 0, so row 1, column 1 = 0. The 6–0 finishes the grid, running horizontal at row 1: 6 at column 0 (an empty-type cell with no constraint), 0 at column 1 ✓.
🔧 Step-by-Step Answer Walkthrough For Medium Level
Three cells at the bottom of the grid must all show the same pip value. This is far more restrictive than a standard two-cell equals pair. Before working any sum arithmetic, ask: which pip value can appear three times simultaneously, given the dominoes in the set?
The only double in the set with high identical pips is 6–6. Place it horizontal across the bottom two cells (row 3, columns 0–1) — both equal 6. The third equals cell (row 3, column 2) must also be 6. Find a domino with a 6-end that can reach column 2 from above.
The 5–6 domino covers the third equals cell with its 6-end at row 3 and its 5-end descending to row 4. The row 4 cell carries a greater-than-1 constraint: 5 > 1 ✓. The three-cell equals region is fully resolved at value 6.
Row 0, column 1 and row 1, column 1 must sum to 7. The 0–3 domino runs horizontal at row 0 with 3 at column 1 and 0 at column 2, contributing 3. So row 1, column 1 must be 4. The 4–5 domino fits horizontal at row 1: 4 at column 1, 5 at column 0. That also locks the equals pair at column 0, rows 1–2: row 2, column 0 must be 5, filled by the 5-end of the 1–5 domino (5 at column 0, 1 at column 1).
Row 2, columns 1–2 must sum to 7. Row 2, column 1 = 1 (from 1–5). So row 2, column 2 = 6: the 1–6 domino runs vertically at column 2, rows 1–2 (1 at row 1, 6 at row 2), giving 1+6=7 ✓. The less-than-7 pair at row 1, columns 2–3: 1+5=6 < 7 ✓. The 0–5 domino fills the top-right area (0 at row 0 column 3, 5 at row 1 column 3), and 0 at row 0 column 2 (from 0–3) matches 0 at row 0 column 3, confirming the top equals pair ✓.
🔧 Step-by-Step Answer Walkthrough For Hard Level
A region covering four cells — at rows 0–2, column 1–2 area — has a sum ceiling of less than 2. The total of all four pips must be 0 or 1. Since even a single 2-pip would push the sum to at least 2 if accompanied by anything nonzero, the only viable solution is all four cells equal 0. These four positions are your forced starting pips.
The 0–0 double covers two of those cells vertically (rows 1–2, column 2) — both 0. The 0–1 domino covers row 0: place it with 0 at column 1 and 1 at column 0. The 2–0 domino covers column 2, row 0: place it with 0 at column 2 and 2 extending right to column 3. All four cells in the less-than-2 region are now 0 ✓.
Row 0, column 0 and row 1, column 0 must sum to 2. Row 0, column 0 = 1 (from the 0–1 domino). So row 1, column 0 = 1, filled by the 2–1 domino running vertically at column 0, rows 1–2 (1 at row 1, 2 at row 2). Next, rows 2–3 at column 0 must also sum to 2: row 2, column 0 = 2 (from 2–1). So row 3, column 0 = 0, filled by the 6–0 domino running vertically at column 0, rows 3–4 (0 at row 3, 6 at row 4).
Row 0, columns 3–4 must sum to 5. Row 0, column 3 = 2 (from the 2–0 domino). So row 0, column 4 = 3, from the 3–4 domino running vertically at column 4, rows 0–1 (3 at row 0, 4 at row 1). Then rows 1–2 at column 4 must also sum to 5: row 1, column 4 = 4 (just placed). So row 2, column 4 = 1, from the 6–1 domino running vertically at column 4, rows 2–3 (1 at row 2, 6 at row 3).
Rows 3–4 at column 4 must sum to 9 — the maximum achievable. Row 3, column 4 = 6 (from 6–1 already placed). So row 4, column 4 = 3, from the 6–3 domino running vertically at column 4, rows 4–5 (3 at row 4, 6 at row 5). 6+3=9 ✓.
Rows 3–4 at column 2 must show equal pips. The 3–3 double fits vertically here — both cells equal 3, no arithmetic required ✓. Finally, the bottom row: rows 6, columns 0–1 must sum to 8. The 6–4 domino at column 0, rows 5–6 places 4 at row 6. The 4–2 domino runs horizontal at row 6, columns 1–2 (4 at column 1, 2 at column 2): 4+4=8 ✓. Columns 2–3 at row 6 must sum to 4: row 6, column 2 = 2. The 2–6 domino runs horizontal at row 6, columns 3–4 (2 at column 3, 6 at column 4): 2+2=4 ✓. The 6 at column 4 carries an empty-type constraint — no restriction ✓.
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