Max & Min Heaps in Java

Part 1 provides a base class with functions common to max heap and min heap.

Part 2 below provides code for Min Heap construction, removal of an element and finding the kth smallest element from the heap.

Part 3 below provide code for Max heap construction, removal of an element and finding the kth largest element from the heap.

Part 1: Class with common functions of heap (get parent, printing etc)

import java.util.ArrayList;
public class Heap {

 ArrayList heap = new ArrayList(); 
 
 int parentIndex(int index) {
  return (index-1)/2;
 } 
 int getParent(int index)  {
  return heap.get(parentIndex(index));
 }
 int getLeftIndex(int index) {
  return (2*index + 1);
 }
 int getRightIndex(int index) {
  return (2*index + 2);
 }
 boolean validIndex(int index){
  return (index>= 0 && index< heap.size()) ? true: false;
 }
 void swap(int index1, int index2)  {
  int temp = heap.get(index1);
  heap.set(index1, heap.get(index2));
  heap.set(index2, temp);
 }
 
 void printHeap(){
  System.out.println(heap);
 }
}

Part 2: Min Heap & Getting kth smallest element

public class MinHeap extends Heap{

 int minHeapify(int index) {
  while(index!= 0 && getParent(index) > heap.get(index)){
   swap(parentIndex(index), index);
   index = parentIndex(index);
  }
  return index;
 }

 void insert(int[] input) {
  int index=heap.size() -1;
  for(int i=0; i< input.length; i++){
   heap.add(input[i]); index++;
   minHeapify(index);
  }
 }

 void siftDown(int pos)
 {
  int minIndex, rightIndex;
  while(validIndex(getLeftIndex(pos)))
  {
   minIndex = getLeftIndex(pos);
   rightIndex = getRightIndex(pos);
   if(validIndex(rightIndex) && heap.get(rightIndex) < heap.get(minIndex))
   {
    minIndex = rightIndex;
   }
   if(heap.get(pos) > heap.get(minIndex))
   {
    swap(pos, minIndex);
    pos = minIndex;
   }
   else break;
  }
 }

 boolean remove(int pos)
 {
  if(!validIndex(pos)) return false;
  if(pos == (heap.size()-1)) {
   heap.remove(pos);
   return true;
  }
  swap(pos, heap.size() -1);
  heap.remove(heap.size()-1);
  pos = minHeapify(pos);
  siftDown(pos);
  return true;
 }
 
 int getKthMin(int k)
 {
  if(k > heap.size()) return -1;
  if(k == 1) return heap.get(0);
  remove(0);
  return getKthMin(k-1);
 }

 public static void main(String[] args) {

  int[] input = {4,6,10,9,8,1,0};
  MinHeap obj = new MinHeap();
  obj.insert(input);
  obj.printHeap();
//  obj.remove(6);
  System.out.println(obj.getKthMin(4));
 }

Part 3: Max heap & get the kth largest element

public class MinHeap extends Heap{
 int minHeapify(int index)
 {
  while(index!=0 && getParent(index) > heap.get(index))
  {
   swap(parentIndex(index), index);
   index = parentIndex(index);
  }
  return index;
 }

 void insert(int[] input)
 {
  int index=heap.size() -1;
  for(int i=0; i< input.length; i++)
  {
   heap.add(input[i]); index++;
   minHeapify(index);
  }
 }

 void siftDown(int pos)
 {
  int minIndex, rightIndex;
  while(validIndex(getLeftIndex(pos)))
  {
   minIndex = getLeftIndex(pos);
   rightIndex = getRightIndex(pos);
   if(validIndex(rightIndex) && heap.get(rightIndex) < heap.get(minIndex))
   {
    minIndex = rightIndex;
   }
   if(heap.get(pos) > heap.get(minIndex))
   {
    swap(pos, minIndex);
    pos = minIndex;
   }
   else break;
  }
 }

 boolean remove(int pos)
 {
  if(!validIndex(pos)) return false;
  if(pos == (heap.size()-1)) {
   heap.remove(pos);
   return true;
  }
  swap(pos, heap.size() -1);
  heap.remove(heap.size()-1);
  pos = minHeapify(pos);
  siftDown(pos);
  return true;
 }
 
 int getKthMin(int k)
 {
  if(k > heap.size()) return -1;
  if(k == 1) return heap.get(0);
  remove(0);
  return getKthMin(k-1);
 }

 public static void main(String[] args) {

  int[] input = {4,6,10,9,8,1,0};
  MinHeap obj = new MinHeap();
  obj.insert(input);
  obj.printHeap();
//  obj.remove(6);
  System.out.println(obj.getKthMin(4));
 }