A sorting quiz asks players to drag items into order. To score an answer, the app counts how many pairs are backwards: pairs of positions i < j where ranks[i] > ranks[j].
Write countBackwardPairs(ranks) that returns that number. Lists can have up to 100,000 items, so checking every pair is too slow; aim for O(n log n). Equal values do not form a backwards pair.
Input: ranks = [2,4,1,3,5] Output: 3
The backwards pairs are (2, 1), (4, 1), and (4, 3).
Input: ranks = [1,2,3,4] Output: 0
A sorted list has no backwards pairs.
0 <= ranks.length <= 100000-10^9 <= ranks[i] <= 10^9Run tries your code on the examples. Submit runs every test, including hidden edge cases, and solves the problem when they all pass.
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I'm here to help with #193 Count Out-of-Order Rankings. I give hints, never the solution, so you get to solve it yourself. Ask for a hint, select code to ask about it, or press Ask Tuto why on a failing test.
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