Comparisons
Merge Sort vs Heap Sort
Updated June 8, 2026 • 5 min read
Merge Sort vs Heap Sort is a comparison of two algorithms that both guarantee O(n log n) on every input, yet differ sharply on memory use and stability. If you have ruled out Quick Sort because you need worst-case guarantees, these two are your main options.
Side by side
| Property | Merge Sort | Heap Sort |
|---|---|---|
| Time (all cases) | O(n log n) | O(n log n) |
| Space | O(n) | O(1) |
| Stable | Yes | No |
| Cache locality | Good (sequential) | Poor (scattered) |
When to choose each
Choose Merge Sort when you need stability or are sorting linked lists or external data. Choose Heap Sort when memory is tight and you need O(1) extra space with a worst-case guarantee. In practice Merge Sort (as Tim Sort) is more common because stability is frequently required.
Frequently asked questions
Which uses less memory, Merge Sort or Heap Sort? +
Heap Sort uses O(1) extra space, far less than Merge Sort's O(n) buffer. If memory is the constraint, Heap Sort wins.
Which is stable, Merge Sort or Heap Sort? +
Merge Sort is stable; Heap Sort is not. If you need to preserve the order of equal elements, choose Merge Sort.
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