4 ms·
> Choose which digit to put diagonally opposite the 1 in the lower right box (3 choices) There are only two choices there. You cannot put a 1, nor the digit (3
by Someone 20d ago
> Choose which digit to put diagonally opposite the 1 in the lower right box (3 choices)
There are only two choices there. You cannot put a 1, nor the digit (3 or 4) that’s in the top the column where you try to put the number.
> Is there a nicer way which makes it obvious that there is exactly one solution for each choice in the last step?
There isn’t. You may end up with a degree of freedom after step 4
1234 1234
..1. ..1.
...1 ...1
.1.. .14.
leads to
1234
..12
..21
2143
which allows for 2 solutions:
1234 1234
3412 4312
4321 3421
2143 2143
- antonTobi 20d agoMy procedure starts with filling the top-left box, not the top row. So it looks something like this after the third step: 12.. 34.1 .1.x ..1. From here x can be any of [2,3,4], and each yields exactly one solution!