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$ curl repovive.com/roadmaps/fundamental-algorithms/divide-and-conquer/counting-inversions-merge

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$ curl repovive.com/roadmaps/fundamental-algorithms/divide-and-conquer/counting-inversions-merge

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Counting Inversions - Merge - Divide and Conquer | Fundamental Algorithms | Repovive

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Fundamental Algorithms8 sections · 294 units2h total

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Counting Inversions - Merge

The merge step that counts inversions.

Merge step counts cross-inversions while merging sorted halves. When $R[j] < L[i]$ , all remaining $L$ elements form inversions with $R[j]$ . Add L.length - i to count.

while i < L.length and j < R.length:
    if L[i] <= R[j]:
        arr[k] = L[i]; i++
    else:
        arr[k] = R[j]
        inversions += L.length - i
        j++
    k++

Copy remaining elements after the loop.