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4
votes
Non-attacking “brooks” on a periodic chess board
For fixed $n$, you can solve the problem via integer linear programming as follows. Let $C_k$ be the set of cells in clique $k$ (row, column, or wrapped diagonal). … The problem is to maximize $\sum_i \sum_j x_{ij}$ subject to linear constraints
$$\sum_{(i,j)\in C_k} x_{ij} \le 1 \quad \text{for all $k$}$$
For $n=8$, the maximum turns out to be
For general $n$, …
1
vote
Accepted
How to put uniformly k objects into n cells?
You can solve the problem via integer linear programming as follows. Let $p_{ij}$ be the priority for assigning object $i$ to cell $j$. …
4
votes
What is the greatest possible number of empty squares that could remain after the jumps?
You can solve the problem via integer linear programming as follows. Let $S=[5] \times [5]$ be the set of squares. … It turns out that the linear programming relaxation (obtained by relaxing the decision variables as $x_{ij} \ge 0$ and $y_{ij\bar{i}\bar{j}} \ge 0$) yields the same optimal objective value, and the corresponding …
3
votes
Individual pangram lists for words of lengths 12-letter, 13-letter, 14-letter, and 15-letter
Via integer linear programming (specifically, set covering), here are the minimum numbers of (YAWL) words to cover every letter at least once:
12:
13:
14:
15: …
1
vote
Accepted
An 18-Letter Challenge-B: three 6-letter words, with limitations
Via integer linear programming, the maximum number of unique letters is
There are $520$ such solutions.
If you disallow the repeated letter to be a vowel, there are …
2
votes
Accepted
An 18-Letter Challenge-A: three 6-letter words, with limitations
Via integer linear programming, the unique solution is …
2
votes
Perfect Pangram development
Via integer linear programming (https://puzzling.stackexchange.com/a/123475/65277), here are the largest numbers of covered letters.
3 3 5 5 5 5
6 6 7 7
5 5 8 8
4 4 9 9 …
2
votes
Accepted
Ying Yang 12x12 - Colombian Sudoku
Via integer linear programming, using the formulation described in my answer https://puzzling.stackexchange.com/a/128031/65277: …
2
votes
Accepted
Pinwheels - Colombian Sudoku
You can solve the problem via integer linear programming as follows, with binary decision variables $x_{ijk}$ to indicate whether cell $(i,j)$ contains digit $k$:
For each region (row, column, or $2\times4 …
3
votes
Can you use all 26 letters across four 7-letter words?
Via integer linear programming (https://puzzling.stackexchange.com/a/123475/65277), I found that the maximum is
There are 515 such optimal solutions, such as: …
6
votes
Accepted
Destroying Democracy
Via integer linear programming, I found the following minimum values for $n \times n$ grids:
Minimum values for $n \le 44$ are here: https://oeis.org/A365271
8x8:
9x9:
10x10:
11x11:
12x12: …
6
votes
The minimal Anti-Sudoku
As a warm-up, here's the lexicographically minimal Sudoku, obtained via integer linear programming, with binary decision variables $x_{ijk}$ to indicate whether cell $(i,j)$ contains digit $k$:
For each …
6
votes
What is the maximum number of people who speak only 1 language?
You can solve the problem via integer linear programming, with a nonnegative decision variable $x_S$ for each of the seven nonempty subsets $S$ of the three languages and linear constraints to enforce … programming relaxation also has maximum value
and the corresponding dual variables provide a short certificate of optimality as follows. …
5
votes
Fill the grid subject to product, sum and knight move constraints
You can solve the problem via integer linear programming as follows. …
13
votes
Is this puzzle solvable? Choose 6 five-letter words to get maximum score
Here's one that omits only X, obtained via integer linear programming:
For the 2315 common words from the list provided in What is the longest Wordle game? …