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Finding Specific Order Statistics with O(n log(n/k)) Complexity
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orderlogwithfindingstatisticsspecificcomplexity
Problem
I'm working on a problem where I need to find specific order statistics in a set of numbers. Given
My Attempt:
So far, I've considered using modified sorting algorithms and heap structures, but I'm not sure if these approaches can achieve the desired time complexity. I suspect there might be a more efficient way to find these specific elements without fully sorting the entire array.
Question:
Can anyone suggest an algorithm or method to find these elements with the required time complexity?
n numbers, I want to determine the k-th smallest, the 2k-th smallest, and so on, up to the ⌊n/k⌋-th smallest element. I'm looking for a method to accomplish this with a time complexity of O(n log(n/k)).My Attempt:
So far, I've considered using modified sorting algorithms and heap structures, but I'm not sure if these approaches can achieve the desired time complexity. I suspect there might be a more efficient way to find these specific elements without fully sorting the entire array.
Question:
Can anyone suggest an algorithm or method to find these elements with the required time complexity?
Solution
Find
Partition the array in almost equal halves about this
Run the algorithm recursively on the two halves. Once the algorithm finds all the required $n/k$ elements; return.
Note that the height of the recurrence tree is $O(\log(n/k))$. and in each level the algorithm is doing $O(n)$ comparison operations.
Thus, the overall running time is $O(n \log (n/k))$.
n/2k-th in $O(n)$ time. There are standard algorithms for finding any p-th smallest element in array in $O(n)$ time.Partition the array in almost equal halves about this
n/2k-th smallest element.Run the algorithm recursively on the two halves. Once the algorithm finds all the required $n/k$ elements; return.
Note that the height of the recurrence tree is $O(\log(n/k))$. and in each level the algorithm is doing $O(n)$ comparison operations.
Thus, the overall running time is $O(n \log (n/k))$.
Context
StackExchange Computer Science Q#164963, answer score: 2
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