91 lines
2.6 KiB
Java
91 lines
2.6 KiB
Java
package be.brainbaking.sorting;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.stream.Collectors;
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public class HeapSort implements Sortable {
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private String asString(List<Integer> list) {
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return list.stream().map(i -> i.toString()).collect(Collectors.joining(", "));
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}
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/**
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* heap-size[A] <- length[A]
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* for i <- |length[A]/2| downto 1
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* do MAX-HEAPIFY(A, i)
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*/
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protected List<Integer> buildMaxHeap(List<Integer> list) {
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System.out.println("to maxify: " + asString(list));
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List<Integer> heapList = new ArrayList<>(list);
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int halfIndex = (int)Math.floor(list.size() / 2);
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for(int i = halfIndex; i >= 1; i--) {
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maxHeapify(heapList, i);
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}
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System.out.println("maxified: " + asString(heapList));
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return heapList;
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}
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private int leftIndex(int index) {
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return index * 2;
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}
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private int rightIndex(int index) {
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return leftIndex(index) + 1;
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}
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private int parentIndex(int index) {
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return (int)Math.floor(index / 2);
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}
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private void maxHeapify(List<Integer> list, int oneBasedIndex) {
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int lefti = leftIndex(oneBasedIndex);
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int righti = rightIndex(oneBasedIndex);
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int largesti = oneBasedIndex;
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if(lefti <= list.size() && list.get(lefti - 1) > list.get(oneBasedIndex - 1)) {
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largesti = lefti;
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}
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if(righti <= list.size() && list.get(righti - 1) > list.get(largesti - 1)) {
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largesti = righti;
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}
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if(largesti != oneBasedIndex) {
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swap(list, oneBasedIndex, largesti);
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maxHeapify(list, largesti);
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}
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}
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private void swap(List<Integer> list, int oneBasedA, int oneBasedB) {
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int temp = list.get(oneBasedA - 1);
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list.set(oneBasedA - 1, list.get(oneBasedB - 1));
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list.set(oneBasedB - 1, temp);
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}
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/**
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* BUILD-MAX-HEAP(A)
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* for i <- length[A] downto 2
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* do exchange A[1] with A[i]
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* heap-size[A] <- heap-size[A] - 1
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* MAX-HEAPIFY(A, 1)
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*/
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@Override
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public List<Integer> sort(List<Integer> list) {
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List<Integer> heap = buildMaxHeap(list);
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List<Integer> sorted = new ArrayList<>();
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for(int i = heap.size(); i >= 1; i--) {
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// in plaats van te swappen met 1, i pitsen we het hoofd van de tree er af
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// ik wil niet heap-size manipuleren en doorgeven
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sorted.add(0, heap.get(0));
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heap.remove(0);
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maxHeapify(heap, 1);
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}
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System.out.println("sorted: " + asString(sorted));
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return sorted;
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}
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}
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