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What is a stable sorting algorithm?

Q: What is a stable sorting algorithm?

**Intuition.** A sort is **stable** if elements that compare *equal* keep their original relative order. It only matters when records carry more than the sort key — e.g. sorting people by age shouldn't scramble the order they were already in by name. sort by number; the letters track original order 3a <text x="140" y="50" fill

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Explain sort stability.

stabilitysorting

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Stable multi-key sort

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people = [("Bob", 30), ("Ann", 25), ("Cy", 30), ("Dan", 25)]

# sort by age; Timsort is stable, so equal ages keep input order
by_age = sorted(people, key=lambda p: p[1])

# --- demo --- Ann before Dan, Bob before Cy (input order preserved)
print(by_age)   # [('Ann', 25), ('Dan', 25), ('Bob', 30), ('Cy', 30)]

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