N-Queens
Place one queen per row; a column or diagonal conflict forces backtracking.
Decision · step 2 of 32Backtracking: 4 queens, with backtracking
Row 0, square (0, 0): no queen shares its column or a diagonal. Place a queen and move to row 1.
What you will see
Queens placed row by row on a board; attacked squares are shaded; a dead row lifts the previous queen.
Cost
| Best | O(n!) |
|---|---|
| Average | O(n!) |
| Worst | O(n!) |
| Space | O(n) |
How you work with it here
play it through, step one change at a time, scrub to any step, run it on your own input, predict what happens next.
Screen readers: Each node of the decision tree announces the choice made and whether it led to success, failure or further choices.
Reduced motion: Tree nodes appear and grey out in place; no travelling focus.
Before this
Taught by the same lesson
Backtracking covers these too, in the same run.