bucket sort
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package be.brainbaking.sorting;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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public class BucketSort implements Sortable {
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private final InsertionSort insertionSorter;
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public BucketSort() {
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this.insertionSorter = new InsertionSort();
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}
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/**
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* n <- length[A]
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* for i <- 1 to n
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* do insert A[i] into list B[n*A[i]] rounded down
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* for i <- 0 to n - 1
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* do sort list B[i] with insertion srot
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* concatenate lists B[0], B[1], ..., B[n - 1] together
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* @param list A
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* @return sorted list
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*/
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@Override
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public List<Integer> sort(List<Integer> list) {
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int n = list.size();
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List<List<Integer>> buckets = initializeBuckets(n);
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for(int i = 1; i <= n; i++) {
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int x = list.get(i - 1);
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int bucketIndex = calculateBucketIndex(n, x);
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if(buckets.size() <= bucketIndex) {
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buckets.add(bucketIndex, Arrays.asList(x));
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} else {
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buckets.get(bucketIndex).add(x);
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}
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}
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return mergeSortedBuckets(buckets);
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}
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private List<Integer> mergeSortedBuckets(List<List<Integer>> buckets) {
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List<Integer> sorted = new ArrayList<>();
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for (List<Integer> bucket : buckets) {
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sorted.addAll(insertionSorter.sort(bucket));
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}
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return sorted;
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}
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private List<List<Integer>> initializeBuckets(int n) {
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List<List<Integer>> buckets = new ArrayList<>();
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for(int i = 0; i < n; i++) {
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buckets.add(new ArrayList<>());
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}
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return buckets;
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}
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/**
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* bucket sorting gaat uit van een uniforme distributie waarbij 0 <= A[i] <= 1
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* deel x door 10 in dit simpel voorbeeld.
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*/
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private int calculateBucketIndex(int n, int x) {
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return (int)Math.floor(n * ((double) x / 10));
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}
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}
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@ -6,6 +6,8 @@ import java.util.List;
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public class InsertionSort implements Sortable {
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public List<Integer> sort(List<Integer> list) {
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if(list.size() == 0) return list;
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// not the same thing, I don't want to mutate the incoming list.
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// start with nothing and insert it into the right position of result list.
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// ex. https://www.geeksforgeeks.org/insertion-sort/
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@ -8,6 +8,11 @@ import java.util.List;
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public class SortTest {
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@Test
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public void bucketSort() {
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simpleTestCaseFor(new BucketSort());
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}
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@Test
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public void quickSort() {
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simpleTestCaseFor(new QuickSort());
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