mgs/median-comparison
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using size_t (uint32) instead of int because only use positive values

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incredibleLeitman 2020-10-06 16:28:39 +02:00
parent 1883659921
commit f3688bbc7f
2 changed files with 36 additions and 20 deletions
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26
MedianQuicksort.h
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@ -1,10 +1,10 @@
#pragma once
int partition(std::vector<size_t>& values, int left, int right) {
int pivotIndex = left + (right - left) / 2;
int pivotValue = values[pivotIndex];
int i = left, j = right;
int temp;
size_t pivotPartition(std::vector<size_t>& values, size_t left, size_t right) {
size_t pivotIndex = left + (right - left) / 2;
size_t pivotValue = values[pivotIndex];
size_t i = left;
size_t j = right;
while (i <= j) {
while (values[i] < pivotValue) {
i++;
@ -13,9 +13,7 @@ int partition(std::vector<size_t>& values, int left, int right) {
j--;
}
if (i <= j) {
temp = values[i];
values[i] = values[j];
values[j] = temp;
std::swap(values[i], values[j]);
i++;
j--;
}
@ -23,18 +21,16 @@ int partition(std::vector<size_t>& values, int left, int right) {
return i;
}
void quicksort(std::vector<size_t>& values, int left, int right) {
void quicksort(std::vector<size_t>& values, size_t left, size_t right) {
if (left < right) {
int pivotIndex = partition(values, left, right);
size_t pivotIndex = pivotPartition(values, left, right);
quicksort(values, left, pivotIndex - 1);
quicksort(values, pivotIndex, right);
}
}
size_t getMedian(std::vector<size_t> values) {
//std::qsort(numbers); // only takes array param
size_t getQuicksortMedian(std::vector<size_t> values, size_t i) {
//std::qsort(numbers); // only takes array param -> custom implementation with vector
quicksort(values, 0, values.size() - 1);
size_t idxMed = values.size() / 2;
if (idxMed - (int)idxMed > 0) idxMed++;
return values[idxMed];
return values[i];
}

30
main.cpp
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@ -4,23 +4,43 @@
#include "fileHandler.h"
#include "Timing.h"
#include "MedianQuicksort.h"
#include "MedianOfMedians.h"
#include "RandomizedSelect.h"
int main(int argc, char** argv) {
// read test values from input file
Timing::getInstance()->startRecord("init");
std::vector<size_t> numbers = readFromFile("testdata");
std::cout << "read " << numbers.size() << " values" << std::endl;
std::cout << "just read " << numbers.size() << " values" << std::endl;
Timing::getInstance()->stopRecord("init");
// index of median -> if odd count +1
size_t idxMed = numbers.size() / 2;
std::cout << "median = " << idxMed << std::endl;
if (idxMed - (int)idxMed > 0) idxMed++;
// vollständige Sortierung mit Quicksort und Ausgabe des mittleren Elements
Timing::getInstance()->startRecord("quicksort");
std::cout << "quicksort median: " << getMedian(numbers) << std::endl;
std::cout << "quicksort median: " << getQuicksortMedian(numbers, idxMed) << std::endl;
Timing::getInstance()->stopRecord("quicksort");
// vorgestellter Randomzized - Select rekursiv implementiert
Timing::getInstance()->startRecord("randomized select");
std::cout << "randomized select: " << randomizedSelect(numbers, 0, numbers.size() - 1, idxMed) << std::endl;
Timing::getInstance()->stopRecord("randomized select");
// ein weiterer Median - Algorithmus aus der Literatur
Timing::getInstance()->startRecord("median of medians");
std::cout << "median of medians: " << getMedianOfMedians(numbers, idxMed) << std::endl;
Timing::getInstance()->stopRecord("median of medians");
// noch ein ein weiterer Median - Algorithmus weil wir so cool sind
Timing::getInstance()->startRecord("wirth");
Timing::getInstance()->stopRecord("wirth");
// Verwendung des C++ STL function templates nth_element
Timing::getInstance()->startRecord("nth element");
std::nth_element(numbers.begin(), numbers.begin() + numbers.size() / 2, numbers.end());
size_t idxMed = numbers.size() / 2;
if (idxMed - (int)idxMed > 0) idxMed++;
std::nth_element(numbers.begin(), numbers.begin() + idxMed, numbers.end());
std::cout << "nth element: " << numbers[idxMed] << std::endl;
Timing::getInstance()->stopRecord("nth element");