TAOCP 7.2.2.1 Exercise 445
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Section 7.2.2.1: Dancing Links
Exercise 445. ▶ [M22] It's surprisingly difficult to construct a valid hitori puzzle that has no seeds. In fact, there are no $n \times n$ examples for $n \le 9$ except when $n = 6$. But it turns out that quite a few seedless $6 \times 6$ hitori puzzles do exist.
Consider the five hitori covers below. Determine, for each of them, the exact number of valid hitori puzzles with no seeds, having that pattern of white and black cells as the solution. Hint: In some cases the answer is zero.
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Solve time: 1m49s
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