# QuickSort & MergeSort
Confidence: high
Last verified: 2026-05-22
Generation: human_only


## TL;DR

QuickSort: average O(n log n), worst O(n²), in-place, not stable. Picks pivot, partitions, recurses. MergeSort: always O(n log n), stable, O(n) auxiliary space. Most practical sorts are hybrid (Timsort=merge+insertion).

## Core Explanation

QuickSort pivot selection: median-of-three reduces worst-case probability. MergeSort is ideal for linked lists (no extra space for merge). Timsort (Python, Java, V8 JS) exploits natural runs in data: O(n) on already-sorted input. Comparison-based sorting lower bound: Ω(n log n). Non-comparison: counting sort, radix sort — O(n) when data range is limited.

## Further Reading

- [Algorithms (4th Edition)](undefined)