🔧 Step-by-Step Answer Walkthrough For Easy Level
Scanning the five dominoes, pip-1 and pip-3 each appear exactly four times. The four-cell equals region in the top row could hold either. Neither is ruled out by the constraint label itself — you need to check which one produces valid domino pairings with the neighboring constraints.
If the four top cells hold 1-pip, the 2×2 block below must be filled from what remains: 3,3,3,6,3,5. Four 3s could fill it, leaving 6 and 5 for the corner and far-right cell. The corner cell [0,0] (> 4) is adjacent to [1,0] which would hold 3 — requiring a [6,3] or [3,6] domino. That domino doesn't exist in the set; only [1,6] is available. Dead end: pip-1 cannot fill the top row.
With pip-3 in the four top cells, the remaining four 1-pips go to the 2×2 block. Two values remain unplaced: 6 and 5. The corner [0,0] connects to [1,0] (= 1 in the block), so the domino must be [1,6] oriented vertically — [0,0]=6 satisfies 'greater than 4'. The far-right cell [1,4] gets 5, satisfying 'less than 6', via [3,5] oriented vertically with the 3-end on top.
Domino [3,3] covers [0,2]–[0,3] horizontally (both = 3). Domino [1,3] covers [1,1]–[0,1] vertically: 1 at [1,1] (inside the 2×2 block), 3 at [0,1] (completing the top equals chain). Domino [1,1] covers [2,0]–[2,1] horizontally: both = 1. The full 2×2 block [1,0]=1, [1,1]=1, [2,0]=1, [2,1]=1 satisfies the equals constraint ✓.
🔧 Step-by-Step Answer Walkthrough For Medium Level
One region contains exactly one cell and carries a sum-of-6 constraint. A single-cell sum region is already solved — the cell must equal the target. Here, [1,0] = 6. Among the six dominoes, only [6,2] carries a 6-pip. It sits vertically: 6 at [1,0], 2 at [2,0].
[2,0] = 2 from Step 1. It sits inside the two-cell sum-of-6 region [2,0],[2,1]. 6 − 2 = 4, so [2,1] = 4. Domino [2,4] covers [3,1]–[2,1] vertically: 2 at [3,1] (extending into the bottom 'less than 4' row), 4 at [2,1] ✓.
The 'less than 4' region covers [3,1] and [3,2]. [3,1] = 2 (< 4 ✓) from Step 2. Domino [0,3] handles [3,2]–[2,2] vertically: 0 at [3,2] (< 4 ✓), 3 at [2,2].
Lower-right sum pair [2,2],[2,3]: [2,2] = 3, so [2,3] = 3 (6−3=3). Domino [4,3] covers [1,3]–[2,3] vertically: 4 at [1,3], 3 at [2,3]. Upper-right sum pair [1,2],[1,3]: [1,3] = 4, so [1,2] = 2 (6−4=2). Domino [2,2] covers [1,1]–[1,2] horizontally: [1,1]=2, [1,2]=2. The 'greater than 0' constraint on [1,1] = 2 ✓.
Domino [1,1] is the only one left. It covers [0,1]–[0,2] horizontally: both = 1. The equals constraint on [0,1],[0,2] is satisfied ✓. All six dominoes placed.
🔧 Step-by-Step Answer Walkthrough For Hard Level
Count each pip value's frequency across all twelve dominoes. Pip-0 appears five times: in [5,0],[3,0],[2,0],[6,0],[4,0]. Pip-5 also appears five times: in [5,0],[1,5],[5,5],[2,5]. Both could theoretically fill the five-cell equals region. Two of the region's cells are horizontally adjacent — they must form one domino. You have [5,5] (double-five) but no [0,0] (double-zero). So pip-0 is impossible for the equals region; all five cells = 5.
Domino [5,5] covers [3,4]–[3,5] horizontally: both = 5. Domino [5,0] covers [4,4]–[5,4] vertically: [4,4]=5, [5,4]=0. Domino [1,5] covers [4,6]–[4,5]: [4,6]=1 (satisfying 'greater than 0' ✓), [4,5]=5. Domino [2,5] covers [2,3]–[2,4] horizontally: [2,3]=2 (satisfying 'greater than 1' ✓), [2,4]=5.
[5,4]=0 from Step 2. The two-cell equals [5,4],[6,4] forces [6,4]=0. Domino [4,0] covers [6,5]–[6,4] horizontally: [6,5]=4, [6,4]=0. The three-cell equals [5,6],[6,5],[6,6]: [6,5]=4 forces all three to 4. Domino [4,4] covers [5,6]–[6,6] vertically: [5,6]=4, [6,6]=4 ✓.
The equals constraint links [1,2],[2,2],[3,2]. Three separate dominoes each contribute a 0-end into that column. Domino [2,0] covers [0,2]–[1,2] vertically: [0,2]=2, [1,2]=0. Domino [6,0] covers [2,1]–[2,2] horizontally: [2,1]=6, [2,2]=0. Domino [3,0] covers [3,1]–[3,2] horizontally: [3,1]=3 (empty constraint, no restriction), [3,2]=0. All three column cells = 0 ✓.
[2,1]=6 (from Step 4). Sum-of-10 pair [2,0],[2,1]: [2,0] = 10−6 = 4. Domino [1,4] covers [1,0]–[2,0] vertically: [1,0]=1, [2,0]=4. Sum-of-5 region [0,0],[0,1],[0,2],[1,0]: [0,2]=2, [1,0]=1 already placed, so [0,0]+[0,1] = 5−2−1 = 2. Domino [1,1] covers [0,0]–[0,1] horizontally: [0,0]=1, [0,1]=1 (1+1+2+1=5 ✓). Sum-of-7: domino [4,3] covers [4,2]–[4,3] horizontally: [4,2]=4, [4,3]=3 (4+3=7 ✓). All twelve dominoes placed.
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