How it works
A hidden knight's tour numbers every square of the board from 1 to N. Consecutive numbers always sit one knight's move apart, and no number repeats.
You are shown a few of those numbers and, in the margins, the sum of the hidden numbers in each row and each column. Your task is to restore the whole tour.
Every board is certified to have exactly one solution. On Sundays the grid is completely empty — only the ten sums — and there is still a single answer.
The worked logic
- One. Pick the line — row or column — with the fewest empty cells. Short lines carry the most information.
- Two. Subtract the numbers already placed in that line from its printed sum. What remains must be shared by the empty cells, which bounds each of them.
- Three. Combine that bound with where the knight can go: a candidate only fits if its neighbours in the tour can reach it. Usually one square is forced, and the next line opens up.