Pattern Recognition Drill
Medium Backtracking
The Problem
Place 4 queens on 4x4 board with no two threatening each other.
What approach would you use?
Think about it before scrolling down.
Row by row, try each column. Use sets for occupied columns and diagonals. Prune invalid placements.
Common Trap
Diagonals: row-col identifies one diagonal, row+col the other. Use sets to track both.