Count index pairs
Difficulty: Easy
Return the number of pairs of distinct indices i < j in a list of length n. n is an integer 0..1000.
Examples
001046Constraints
Use the stated representation and return value. Do not mutate inputs. Unless a tighter limit is stated, arrays contain at most 200 integers in -1000..1000; graphs have at most 100 vertices, valid indices and 1000 edges; tree depth is at most 30. No network or file access. Tests support learning; review the implementation to check the requested algorithm.
Review lesson: Complexity and contractsA little nudge
Reveal one hint at a time. Give yourself a moment to try it.
Worked solution
Try your own approach first, then compare the reasoning.
Complexity
Ready when you are
Write your solution, then run it against the practice tests.
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