Find Middle
Slow moves one, fast moves two. When fast runs out, slow is halfway.
Decision · step 2 of 5Fast and Slow Pointers: Find the middle of seven
Step 1: slow moves to 2, fast jumps two to 3.
What you will see
Two pointers race; the fast one reaches the end as the slow one reaches the centre.
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.