71 lines
1.9 KiB
Java
71 lines
1.9 KiB
Java
package be.brainbaking.sorting;
|
|
|
|
import java.util.ArrayList;
|
|
import java.util.Arrays;
|
|
import java.util.List;
|
|
|
|
public class BucketSort implements Sortable {
|
|
|
|
private final InsertionSort insertionSorter;
|
|
|
|
public BucketSort() {
|
|
this.insertionSorter = new InsertionSort();
|
|
}
|
|
|
|
/**
|
|
* n <- length[A]
|
|
* for i <- 1 to n
|
|
* do insert A[i] into list B[n*A[i]] rounded down
|
|
* for i <- 0 to n - 1
|
|
* do sort list B[i] with insertion srot
|
|
* concatenate lists B[0], B[1], ..., B[n - 1] together
|
|
* @param list A
|
|
* @return sorted list
|
|
*/
|
|
@Override
|
|
public List<Integer> sort(List<Integer> list) {
|
|
int n = list.size();
|
|
List<List<Integer>> buckets = initializeBuckets(n);
|
|
|
|
for(int i = 1; i <= n; i++) {
|
|
int x = list.get(i - 1);
|
|
int bucketIndex = calculateBucketIndex(n, x);
|
|
|
|
if(buckets.size() <= bucketIndex) {
|
|
buckets.add(bucketIndex, Arrays.asList(x));
|
|
} else {
|
|
buckets.get(bucketIndex).add(x);
|
|
}
|
|
}
|
|
|
|
return mergeSortedBuckets(buckets);
|
|
}
|
|
|
|
private List<Integer> mergeSortedBuckets(List<List<Integer>> buckets) {
|
|
List<Integer> sorted = new ArrayList<>();
|
|
for (List<Integer> bucket : buckets) {
|
|
sorted.addAll(insertionSorter.sort(bucket));
|
|
}
|
|
|
|
return sorted;
|
|
}
|
|
|
|
private List<List<Integer>> initializeBuckets(int n) {
|
|
List<List<Integer>> buckets = new ArrayList<>();
|
|
|
|
for(int i = 0; i < n; i++) {
|
|
buckets.add(new ArrayList<>());
|
|
}
|
|
|
|
return buckets;
|
|
}
|
|
|
|
/**
|
|
* bucket sorting gaat uit van een uniforme distributie waarbij 0 <= A[i] <= 1
|
|
* deel x door 10 in dit simpel voorbeeld.
|
|
*/
|
|
private int calculateBucketIndex(int n, int x) {
|
|
return (int)Math.floor(n * ((double) x / 10));
|
|
}
|
|
}
|