Sorting algorithms arrange elements in order (ascending, descending, or by a key). The most practical algorithms — quicksort and merge sort — run in O(n log n). Understanding sorting helps with interview prep, but in practice, you'll use built-in sort functions that are already optimized.

How Sorting Algorithm Works

Built-in sorts (Array.sort, Python's sorted) use Timsort — O(n log n), stable, and optimized for real-world data. For interviews, understand: bubble sort (O(n²), simple), merge sort (O(n log n), stable, divide-and-conquer), and quicksort (O(n log n) average, in-place).

Key Concepts

  • O(n log n) — The theoretical lower bound for comparison-based sorting — merge sort, quicksort, heapsort achieve this
  • Stable Sort — Equal elements maintain their original relative order — merge sort and Timsort are stable
  • In-Place — Sorts without extra memory — quicksort is in-place; merge sort requires O(n) extra space
  • Quicksort — Average O(n log n), in-place — the most commonly used sorting algorithm in practice

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Frequently Asked Questions

Which sorting algorithm should I learn?

Merge sort (stable, always O(n log n), great for learning divide-and-conquer) and quicksort (fast in practice, commonly used). Understand bubble sort to know why it's bad.

Do I ever implement sorting?

Almost never. Use your language's built-in sort. But understanding sorting algorithms teaches fundamental CS concepts — divide and conquer, recursion, time/space trade-offs.

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