Opposite Direction Pointers
Start at both ends and move inward. The comparison decides which one moves.
Decision · step 2 of 5Two Pointers: Two sum on a sorted array
1 + 15 = 16, too big. Only a smaller right value can help, so right moves down.
What you will see
Pointers converge from the edges; which one moves depends on the comparison.
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.
Screen readers: Pointers announce their name and index; each step announces which pointer moved and why.
Reduced motion: Pointers appear at their new index with a brief emphasis instead of gliding.
Before this
Taught by the same lesson
Two Pointers covers these too, in the same run.