๐ง Step-by-Step Answer Walkthrough For Easy Level
The region at [0,2] has a sum-2 target and only one cell, so its value must be exactly 2. This is the strongest anchor in the grid and will force an immediate domino placement.
The 2 at [0,2] must come from a domino containing a 2. The only available is [2,3]. Its other cell must cover an adjacent neighbor; the only viable orientation puts the 3 on [0,1] (satisfying the future needs of the sum-8 region).
With [0,1]=3, the sum-8 region demands [1,1]=5. The domino [0,5] is the only 5-bearer; place it vertically with 5 at [1,1] and 0 at [1,0]. Then the sum-1 pair [1,0],[2,0] forces [2,0]=1.
The equals region [2,1],[3,1] means both cells must match. We already have [2,1] as the partner of [2,0]โs 1 โ the [6,1] domino places 6 there and 1 at [2,0]. So [3,1] must be 6; domino [6,3] fits horizontally with 6 at [3,1] and 3 at [3,2] (satisfying greater-2). The last empty pair [1,3],[2,3] takes the [2,2] domino vertically, both 2.
๐ง Step-by-Step Answer Walkthrough For Medium Level
Cells [0,1] and [1,1] must be identical. Scanning the available dominoes, no single tile has two equal numbers, so we need two different dominoes that each supply a matching digit. The only plausible pairing comes from a 2: one from a [2,5] domino covering [0,1] and one from a [1,2] domino hitting [1,1].
Place the [2,5] domino horizontally with 2 at [0,1] and 5 at [0,2]. Now the sum-10 pair [0,2],[1,2] has a 5 on top, so [1,2] must become 5 as well.
Place the [1,2] domino vertically: its 2 lands on [1,1] (matching [0,1]โs 2) and its 1 lands on [2,1], which obeys the empty constraint. This solidifies both the equals bottleneck and the empty cell.
We still need a 5 at [1,2]; the [4,5] domino placed vertically with 5 at [1,2] and 4 at [2,2] does the job. Now the greater-2 single at [0,3] comes into play: it must be >2, so [0,3] gets a 3 from the [0,3] domino, with its 0 partner dropping into [1,3].
The sum-7 region [2,0],[3,0] takes the [3,4] domino vertically with 3 and 4. The sum-10 cell [2,3] needs a 6 to pair with [2,2]โs 4; the [0,6] domino places 6 there and 0 at [2,4]. Finally, the less-4 pair [3,2],[3,3] must be below 4, so the [1,1] domino fills both with 1s horizontally.
๐ง Step-by-Step Answer Walkthrough For Hard Level
Nearly every cell is its own region with a target sum, so write these values immediately: [0,0]=3, [0,1]=0, [0,2]=2, [0,3]=2, [1,1]=1, [1,2]=5, [1,3]=1, [2,3]=1, [3,0]=4, [3,1]=3, [3,2]=4, [3,3]=3, [4,0]=0, [4,1]=2, [4,2]=4, [4,3]=5, [5,0]=3, [5,1]=3, [5,2]=4, [5,3]=1, [6,0]=1, [6,1]=2, [6,2]=4, [6,3]=5, [7,0]=5, [7,1]=5, [7,2]=3, [7,3]>0. The only unconstrained cells are [1,0] and row 2โs [2,0],[2,1],[2,2].
The fixed 1 at [1,1] must pair with an adjacent cell โ [0,1] is already 0, so that would require a [0,1] domino, but [0,1] is already spoken for by the sum-0. Thus [1,1] must pair downward with [2,1], forcing [2,1]=0 via the [0,1] domino. Similarly, the 5 at [1,2] must pair with [2,2]=0 via [0,5], and the 4 at [3,0] needs [2,0]=0 via [0,4]. The three empty row-2 cells become zeros.
Back to the top: [0,1]=0 and [0,2]=2 are neighbors, so place [0,2] domino horizontally. [0,3]=2 and [1,3]=1 are also neighbors; the [1,2] domino fits vertically with 1 on [1,3] and 2 on [0,3]. [0,0]=3 pairs with empty [1,0] via [3,6] vertically, giving [1,0]=6.
With [2,0]=0, place [0,4] vertically to also satisfy [3,0]=4. The sum-0 at [4,0] forces a 0, which pairs with [5,0]=3 using [0,3] vertically. The [3,1]=3 and [3,2]=4 are adjacent, so [3,4] domino goes horizontally. [4,1]=2 and [5,1]=3 are vertically adjacent, so [2,3] goes there.
The pair [4,2]=4 and [4,3]=5 take the [4,5] domino horizontally. [5,3]=1 pairs with [5,2]=4 via [1,4] vertically. Down on the bottom rows: [6,0]=1 and [7,0]=5 need [1,5] vertically; [6,1]=2 and [6,2]=4 take [2,4] horizontally; [7,2]=3 and [7,1]=5 take [3,5] horizontally.
The last unfilled constrained cells are [7,3] (greater 0) and [6,3] (sum 5). The [2,5] domino places 2 at [7,3] and 5 at [6,3], satisfying both. Every sum is now met, and only the [1,3] domino is left. It perfectly covers [2,3]=1 and [3,3]=3 vertically, matching the remaining values.
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