[esquivalience]

This works well for the lower levels but as the grid gets bigger, a refinement stage needs adding to the tiebreak. I suggest switching view from per-square to per-line for tiebreaks. How about this:

Larger grid: 1. take centre and fill diagonals

2. for the first few lines a big grid (say level 5) is big enough that the differences between optimal and not are small, so use "most close to completed" for a few lines

3. After a few lines (I want to say 30% of target?), the "most close to completed" ties will become more relevant. Breaking ties from the focus of one square doesn't work, because the computer's completion could change things.

4. Instead, to break a tie look at the lines that cross the candidate lines. For each number in the candidate, count the Xs that cross it. Sum the Xs for a line to find a value. Do this for each candidate and the most valuable is the candidate to pick.

This works well because even a small difference in value becomes very important towards the end.