Understanding the pivot selection
Quicksort divides the problem by choosing a pivot and arranging elements relative to it. The choice of pivot strongly affects performance: a median pivot splits nearly evenly, while a poor pivot can degrade to quadratic time. Many implementations use the median-of-three heuristic or random selection to avoid pathological inputs.
Once the pivot is chosen, the two-pointer technique scans inward from both ends, swapping elements that are on the wrong side. This in-place rearrangement is the key to quicksort's practical speed and minimal memory overhead.
Recursive divide and conquer flow
After partitioning, the algorithm recursively sorts the left subarray (elements less than pivot) and right subarray (elements greater than pivot). The base case is reached when a subarray has one element or fewer. The elegance lies in the fact that no merge step is needed, unlike mergesort, because the partitioning implicitly orders the pivot into its final position.
With average-case O(n log n) performance and typical in-place behavior, quicksort has remained the preferred choice for general-purpose sorting in production systems for decades.