Recursive solver in Python with backtracking to solve the following Sudoku Twins puzzle that was included with the Dutch newspaper De Volkskrant on Friday 13 October.
In such a Sudoku Twin, the center 3 columns are shared by both the left and right twin. Solving the puzzle then comes down to solving the two 9x9 sudoku's individually as normal, as long as we ensure the center 3 columns have the same values in the left and right "twins".
┌───┬───┬───┰───┬───┬───╔═══╦═══╦═══╗───┬───┬───┰───┬───┬───┐
│ ┊ 8 ┊ ┃ ┊ 1 ┊ ║ ┊ ┊ ║ ┊ ┊ ┃ 2 ┊ 5 ┊ │
│ 5 ┊ ┊ ┃ 9 ┊ ┊ ║ 4 ┊ ┊ ║ ┊ 1 ┊ ┃ ┊ ┊ │
│ 6 ┊ ┊ 2 ┃ 3 ┊ ┊ ║ ┊ ┊ ║ 2 ┊ ┊ ┃ ┊ ┊ 6 │
├━━━┊━━━┊━━━╂━━━┊━━━┊━━━║━━━┊━━━┊━━━║━━━┊━━━┊━━━╂━━━┊━━━┊━━━┤
│ 8 ┊ 2 ┊ ┃ ┊ ┊ 6 ║ ┊ ┊ 9 ║ ┊ ┊ ┃ ┊ ┊ │
│ ┊ ┊ ┃ ┊ 2 ┊ 1 ║ 3 ┊ ┊ 6 ║ 4 ┊ 5 ┊ ┃ ┊ ┊ │
│ ┊ ┊ ┃ ┊ ┊ ║ 8 ┊ ┊ ║ 9 ┊ ┊ ┃ ┊ 1 ┊ 3 │
├━━━┊━━━┊━━━╂━━━┊━━━┊━━━║━━━┊━━━┊━━━║━━━┊━━━┊━━━╂━━━┊━━━┊━━━┤
│ 7 ┊ ┊ ┃ ┊ ┊ 3 ║ ┊ ┊ ║ ┊ ┊ 3 ┃ 8 ┊ ┊ 2 │
│ ┊ ┊ ┃ ┊ 7 ┊ ║ ┊ ┊ 3 ║ ┊ ┊ 5 ┃ ┊ ┊ 4 │
│ ┊ 6 ┊ 3 ┃ ┊ ┊ ║ ┊ ┊ ║ ┊ 4 ┊ ┃ ┊ 3 ┊ │
└───┴───┴───┸───┴───┴───╚═══╩═══╩═══╝───┴───┴───┸───┴───┴───┘
Just Python 3
python3 main.py
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