How many inversions (pairs i a[j]) does the array 8, 4, 2, 1, 9, 3, 7 contain?

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How many inversions (pairs i < j with a[i] > a[j]) does the array 8, 4, 2, 1, 9, 3, 7 contain?

How many inversions (pairs i < j with a[i] > a[j]) does the array 8, 4, 2, 1, 9, 3, 7 contain?

Correct answer: D

Counting greater elements to the right: 8→5 (4,2,1,3,7), 4→3 (2,1,3), 2→1 (1), 9→2 (3,7) = 11.

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