programming-examples/java/Data_Structures/Java Program to Implement Min Heap.java

/*This Java program is to implement Min heap. A Heap data structure is a Tree based data structure that satisfies the HEAP Property “If A is a parent node of B then key(A) is ordered with respect to key(B) with the same ordering applying across the heap.”
So in a Min Heap this property will be “If A is a parent node of B then key(A) is less than key(B) with the same ordering applying across the heap.” and in a max heap the key(A) will be greater than Key(B).*/

public class MinHeap
{
    private int[] Heap;
    private int size;
    private int maxsize;

    private static final int FRONT = 1;

    public MinHeap(int maxsize)
    {
        this.maxsize = maxsize;
        this.size = 0;
        Heap = new int[this.maxsize + 1];
        Heap[0] = Integer.MIN_VALUE;
    }

    private int parent(int pos)
    {
        return pos / 2;
    }

    private int leftChild(int pos)
    {
        return (2 * pos);
    }

    private int rightChild(int pos)
    {
        return (2 * pos) + 1;
    }

    private boolean isLeaf(int pos)
    {
        if (pos >=  (size / 2)  &&  pos <= size)
            {
                return true;
            }
        return false;
    }

    private void swap(int fpos, int spos)
    {
        int tmp;
        tmp = Heap[fpos];
        Heap[fpos] = Heap[spos];
        Heap[spos] = tmp;
    }

    private void minHeapify(int pos)
    {
        if (!isLeaf(pos))
            {
                if ( Heap[pos] > Heap[leftChild(pos)]  || Heap[pos] > Heap[rightChild(pos)])
                    {
                        if (Heap[leftChild(pos)] < Heap[rightChild(pos)])
                            {
                                swap(pos, leftChild(pos));
                                minHeapify(leftChild(pos));
                            }
                        else
                            {
                                swap(pos, rightChild(pos));
                                minHeapify(rightChild(pos));
                            }
                    }
            }
    }

    public void insert(int element)
    {
        Heap[++size] = element;
        int current = size;
        while (Heap[current] < Heap[parent(current)])
            {
                swap(current,parent(current));
                current = parent(current);
            }
    }

    public void print()
    {
        for (int i = 1; i <= size / 2; i++ )
            {
                System.out.print(" PARENT : " + Heap[i] + " LEFT CHILD : " + Heap[2*i]
                                 + " RIGHT CHILD :" + Heap[2 * i  + 1]);
                System.out.println();
            }
    }

    public void minHeap()
    {
        for (int pos = (size / 2); pos >= 1 ; pos--)
            {
                minHeapify(pos);
            }
    }

    public int remove()
    {
        int popped = Heap[FRONT];
        Heap[FRONT] = Heap[size--];
        minHeapify(FRONT);
        return popped;
    }

    public static void main(String...arg)
    {
        System.out.println("The Min Heap is ");
        MinHeap minHeap = new MinHeap(15);
        minHeap.insert(5);
        minHeap.insert(3);
        minHeap.insert(17);
        minHeap.insert(10);
        minHeap.insert(84);
        minHeap.insert(19);
        minHeap.insert(6);
        minHeap.insert(22);
        minHeap.insert(9);
        minHeap.minHeap();
        minHeap.print();
        System.out.println("The Min val is " + minHeap.remove());
    }
}

/*
The Min Heap is
 PARENT : 3 LEFT CHILD : 5 RIGHT CHILD :6
 PARENT : 5 LEFT CHILD : 9 RIGHT CHILD :84
 PARENT : 6 LEFT CHILD : 19 RIGHT CHILD :17
 PARENT : 9 LEFT CHILD : 22 RIGHT CHILD :10
The Min val is 3