Use this tag with questions about the Quickselect algorithm, an algorithm to find the nth smallest member in a list.
Questions tagged [quickselect]
85 questions
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vote
2 answers
choosing pivot for the quickselect using median implemented in java?
I have found this code in github for quickselect algorithm otherwise known as order-statistics. This code works fine.
I do not understand medianOf3 method, which is supposed to arrange the first, middle and last index in sorted order. but actually…
brain storm
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vote
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Python- Quickselect function finding the median
So I have developed the code for a quick select function but it doesn't seem to be printing out the median.
I have the main function prompt for a file name and then import that txt file, split it up into a list of numerals this is the txt…
user123456789101112
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Python Quickselect not printing/returning pivot
Here is the code for quickselect
def quickSelect(lst, k):
if len(lst) != 0:
pivot = lst[(len(lst)) // 2]
smallerList = []
for i in lst:
if i < pivot:
smallerList.append(i)
largerList = []
for i in lst:
…
BLU
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vote
1 answer
My quickselect algorithm is not returning the correct value
So I'm trying to implement a quickselect algorithm in C++ in order to find the median value in a vector, however it is not properly partially-sorting the list and is also not returning the correct median value.
I can't seem to find where the error…
user1782677
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0
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1 answer
Why this quick select algorithm doesn't work always
I have a simple quick select algorithm and want to understand why it doesn't work sometimes.
The question is to find Top K Frequent Elements. I know there are other ways to do it such as using heap or bucket sorting. But I am curios why my algorithm…
Alan
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Median of medians algorithm: why divide the array into blocks of size 5 what if we divide into group of 4 is this effect time complexity
i was little confuse to make recursion (T) what if we divide the array (n/4). and why it is always recommended to use odd division of array why specifically 5. when we divide into 5 the recursion is like this
T(n) <= theta(n) + T(n/5) +…
Sam
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How to translate from Lomuto Partitioning scheme to Hoare's Partition scheme in QuickSelect/QuickSort?
I am working on the problem https://leetcode.com/problems/k-closest-points-to-origin/ with the question statement reproduced here:
Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane and an integer k, return the k…
AndW
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How to calculate median of an unsorted frequency table in O(n)?
I have a dataset comprised of n unsorted tuples representing numbers (let's say specific color codes) and their frequency (number of times of appearance).
I want to find an exact median of the numbers with worst case complexity of O(n).
For…
bashstash
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Quickselect algorithm condition
So I am going through the Quick select algorithm from the CLRS book and I understand the whole concept of the algorithm. But one thing that I am not able to grasp is the initial condition they have at the top. Following is my implementation of the…
0
votes
1 answer
bug in qselect mips assembly program
Below is the quickselect algorithm in mips. There is an error there but I can't find it. qselect function does not work correctly, but the other functions seem to be fine. I have spent so many hours trying to debug it but it compiles without errors…
beginnergrammer
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Finding kth smallest element in array using QuickSelect. Why we should substract L(leftmost index) from POS(position of random partition)?
// function for finding Kth smallest element
int kthSmallest(int arr[], int l, int r, int k)
{
if (k > 0 && k <= r - l + 1)
{
int pos = randPart(arr, l, r); // position of random partition
// now compairing pos with Kth…
anmol065
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0
votes
1 answer
Calls value not incrementing as intended
I am writing a program meant to find the average number of recursive calls it takes to run quickselect, and I have added a counter "calls" to keep track of the number of recursive calls. I have it incrementing every time quickselect is called again,…
Fionnuala
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0
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Time complexity of quickselect algorithm
I am not sure of what will be the time complexity of the Quickselect algorithm (for kth largest element), so can anyone please help me out
def swap(arr,i,j):
temp = arr[i]
arr[i] = arr[j]
arr[j] = temp
def…
saurav
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Find K-th largest element with QuickSelect in Python
I am new in Python and I exercising in writing codes, but I am having some troubles.
I am trying to implement QuickSelect in order to extract the K largest element.
This is my code;
def partition(A, left, right):
pivot = random.randrange(left,…
user15874067
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0
votes
1 answer
Select the K largest elements with QuickSelect - Python
I am new in Python and I exercising in writing codes, but I am having some troubles.
I am trying to implement an algorithm based on QuickSelect in which it's possible to extract the K largest elements.
So, before I implement the QuickSelect…
user15874067
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