Improves on bubble sort by comparing elements far apart, then reducing the gap by a shrink factor of 1.3. This kills "turtles" (small values near the end) that make bubble sort slow.
Worst: O(n²)
Average: O(n²/2^p) ≈ O(n log n)
Best: O(n log n)
Space: O(1)
Watch the arcs: wide gaps shrink to 1, turning into bubble sort for the final cleanup.