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Que – Consider the recursive quicksort algorithm with “random pivoting”. That is, in each recursive call, a pivot is chosen uniformly at random from the sub-array being sorted. When this randomized algorithm is applied to an array of size n all whose elements are distinct, what is the probability that the smallest and the $2^{nd}$ largest elements in the array are compared during a run of the algorithm?


I am getting – $\frac{2}{n}+(\frac{1}{n}*\frac{2}{n-1}) = \frac{2}{n-1} $

Please verify.

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4 Comments

You seem correct to me.
1
1
YES! 2/n-1 is correct. Nice question!
2
2

your approach seems to be correct 2/n-1.

2
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