Remove Nth From End
Lead one pointer n ahead, then walk both until the leader runs out. Trail is just before the target.
Decision · step 4 of 6Fast and Slow Pointers: Remove the 2nd from the end
Both move. Lead at 4, trail at 2.
What you will see
A fixed gap of n between two pointers; when the front one ends, the back one is just before the target.
Cost
| Best | O(n) |
|---|---|
| Average | O(n) |
| Worst | O(n) |
| Space | O(1) |
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, try operations in any order.
Screen readers: Each node announces its value and what it points to; each step announces the pointer change ("node 3 now points to node 5").
Reduced motion: Pointer arrows redraw in place with a brief emphasis instead of animating the detach and reattach.
Before this
Taught by the same lesson
Fast and Slow Pointers covers these too, in the same run.