43 lines
951 B
Python
43 lines
951 B
Python
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"""
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Algorithm Type: Divide & Conquer
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Time Complexity: O(n*log(n))
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"""
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def count_split_inv(arr, left, right):
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split_inv = ridx = lidx = 0
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size = len(arr)
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lsize = len(left)
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rsize = len(right)
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for i in range(size):
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if lidx != lsize and ridx != rsize:
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if right[ridx] <= left[lidx]:
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arr[i] = right[ridx]
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ridx += 1
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split_inv += lsize - lidx
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else:
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arr[i] = left[lidx]
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lidx += 1
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elif lidx == lsize:
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arr[i] = right[ridx]
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ridx += 1
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elif ridx == rsize:
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arr[i] = left[lidx]
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lidx += 1
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return split_inv;
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def count_inversions(arr):
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size = len(arr)
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if size == 1:
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return 0
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mid = int(size/2)
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left = arr[:mid]
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right = arr[mid:]
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l_inv = count_inversions(left)
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r_inv = count_inversions(right)
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split_inv = count_split_inv(arr, left, right)
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return l_inv + r_inv + split_inv
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numbers = [8, 2, 1, 5, 7, 3, 9, 2, 0, 1]
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print(count_inversions(numbers))
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