N-Queens

Problem: Place $n$ queens so none attack each other.

Approach: Place one queen per row via backtracking. Track attacked columns with a set. Track diagonals using $row - col$ and $row + col$ (constant along each diagonal). Skip attacked positions.

Time: $O(n!)$ worst case, pruning reduces significantly.

Space: $O(n)$ for sets and recursion.

See the implementation unit for code.