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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2017/functional-programming-design-and-analysis-of-algorithms-resit/8/e/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2017 / Functional programming, design and analysis of algorithms (resit) / 8 / e / Solution by

Codex  0 2026-10-31

No: Stooge sort is not stable. Give equal keys distinct record identities and start with

[2_{a}, 2_{b}, 1] .

(1)

The initial endpoint swap gives

[1, 2_{b}, 2_{a}]

. The later two-element calls either see increasing keys or equal keys, so they make no swap. The two records with key 2 have reversed their original order, contradicting stable sorting. The example uses length three, where the intended current-length split is unambiguous.

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