An inversion is an array of numbers is any pair (i,j) such
that i<j and A[i]>A[j]. What is the average number of
inversions in an array of n ?
distinct numbers?
Answers were Sorted based on User's Feedback
Answer / narina thakur
The average number of inversions in an array of N distinct
elements is N(N-1)/4
Proof:
Total number of inversions in a list L and its reverse Lr
is N(N-1)/2. Average list has half this amount, N(N-1)/4.
Is This Answer Correct ? | 15 Yes | 6 No |
Answer / vivek sampara
How can you have the reverse of the list when it says i<j
and A[i]>A[j] ?
The Array always starts with A[0] till A[n] .
We cant have it reversed as A[n] to A[0].
The And the sequence of the total number of pairs are
n(n+1)/2
because the pairs are (n,n-1),(n,n-2),(n,n-3).....(n,0)
and (n-1,n-2),(n-1,n-3),(n-1,n-4)......,(n-1,0)
and (n-2,n-3),(n-2,n-4),(n-2,n-5)......,(n-2,0)
the list is n+(n-1)+(n-2)+.....3+2+1+0
reversing we'll get
1+2+3+4.....(n-1)+n =n(n+1)/2
So the average number of inversions are
(n(n+1)/2 )/n
= n(n+1)/2n
Is This Answer Correct ? | 8 Yes | 8 No |
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