Maxheaps.java

class MaxHeap {
    int[] heap;
    int size;
    int capacity;

    MaxHeap(int capacity) {
        this.capacity = capacity;
        this.size = 0;
        heap = new int[capacity];
    }

    void insert(int value) {
        if (size == capacity) {
            System.out.println("IT'S FULL");
            return;
        }
        heap[size] = value;
        heapifyUp(size);
        size++;
    }

    void heapifyUp(int index) {
        while (index > 0 && heap[index] > heap[(index - 1) / 2]) {
            swap(index, (index - 1) / 2);
            index = (index - 1) / 2;
        }
    }

    int delete() {
        if (size <= 0) return -1;
        if (size == 1) {
            size--;
            return heap[0];
        }

        int root = heap[0];
        heap[0] = heap[size - 1];
        size--;
        heapifyDown(0);

        return root;
    }

    void heapifyDown(int i) {
        int largest = i;
        int left = 2 * i + 1;
        int right = 2 * i + 2;

        if (left < size && heap[left] > heap[largest])
            largest = left;

        if (right < size && heap[right] > heap[largest])
            largest = right;

        if (largest != i) {
            swap(i, largest);
            heapifyDown(largest);
        }
    }

    void swap(int i, int j) {
        int temp = heap[i];
        heap[i] = heap[j];
        heap[j] = temp;
    }

    void display() {
        for (int i = 0; i < size; i++) {
            System.out.print(heap[i] + " ");
        }
        System.out.println();
    }
}

public class Maxheaps {
    public static void main(String[] args) {
        MaxHeap h = new MaxHeap(10);
        h.insert(4);
        h.insert(5);
        h.insert(3);
        h.insert(10);
        h.insert(40);

        h.display();
        h.delete();
        h.display();
        h.delete();
        h.display(); 
    }
}