Heaps

Author: kunal-kushwaha

lectures/24-heaps/code/heaps-1/Heap.java

@@ -0,0 +1,85 @@
+import java.util.ArrayList;
+
+class Heap<T extends Comparable<T>> {
+
+ private ArrayList<T> list;
+
+ public Heap() {
+ list = new ArrayList<>();
+ }
+
+ private void swap(int first, int second) {
+ T temp = list.get(first);
+ list.set(first, list.get(second));
+ list.set(second, temp);
+ }
+
+ private int parent(int index) {
+ return (index - 1) / 2;
+ }
+
+ private int left(int index) {
+ return index * 2 + 1;
+ }
+ 
+ private int right(int index) {
+ return index * 2 + 2;
+ }
+
+ public void insert(T value) {
+ list.add(value);
+ upheap(list.size() - 1);
+ }
+ private void upheap(int index) {
+ if(index == 0) {
+ return;
+ }
+ int p = parent(index);
+ if(list.get(index).compareTo(list.get(p)) < 0) {
+ swap(index, p);
+ upheap(p);
+ }
+ }
+
+ public T remove() throws Exception {
+ if (list.isEmpty()) {
+ throw new Exception("Removing from an empty heap!");
+ }
+
+ T temp = list.get(0);
+
+ T last = list.remove(list.size() - 1);
+ if (!list.isEmpty()) {
+ list.set(0, last);
+ downheap(0);
+ }
+ 
+ return temp;
+ }
+ private void downheap(int index) {
+ int min = index;
+ int left = left(index);
+ int right = right(index);
+
+ if(left < list.size() && list.get(min).compareTo(list.get(left)) > 0) {
+ min = left;
+ }
+
+ if(right < list.size() && list.get(min).compareTo(list.get(right)) > 0) {
+ min = right;
+ }
+
+ if(min != index) {
+ swap(min, index);
+ downheap(min);
+ }
+ }
+
+ public ArrayList<T> heapSort() throws Exception {
+ ArrayList<T> data = new ArrayList<>();
+ while(!list.isEmpty()) {
+ data.add(this.remove());
+ }
+ return data;
+ }
+}

lectures/24-heaps/code/heaps-1/Main.java

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+import java.util.ArrayList;
+
+class Main {
+ public static void main(String[] args) throws Exception{
+ Heap<Integer> heap = new Heap<>();
+
+ heap.insert(34);
+ heap.insert(45);
+ heap.insert(22);
+ heap.insert(89);
+ heap.insert(76);
+
+ ArrayList list = heap.heapSort();
+ System.out.println(list);
+
+ }
+}