MinHeap.java

public class MinHeap {
    public static void main(String[] args){
        minHeap heap = new minHeap(10);
        heap.insert(5);
        heap.insert(3);
        heap.insert(17);
        heap.insert(10);
        heap.insert(84);
        heap.insert(19);

        System.out.println("Min: " + heap.extractMin());  //Should print 3 as the min.
    }
    public static class minHeap{
        int[] heap;
        int size;
        int capacity;

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

        private int parent(int i) {return (i - 1) / 2;}
        private int left(int i) {return 2 * i + 1;}
        private int right(int i) {return 2 * i + 2;}

        public void insert(int data){
            if(size == capacity){
                System.out.println("Heap is full!");
                return;
            }
            heap[size] = data;
            heapifyDown(0);
            size++;
        }
        public int extractMin(){
            if(size == 0){
                System.out.println("Heap is Empty!");
            }
            int min = heap[0];
            heap[0] = heap[size -1];
            size--;
            heapifyUp(size);
            return min;
        }
        private void heapifyUp(int i){
            while(i > 0 && heap[parent(i)] > heap[i]){
                swap(parent(i), i);
                i = parent(i);
            }
        }
        private void heapifyDown(int i){
            int smallest = i;
            int l = left(i);

            int r = right(i);

            if(l < size && heap[l] < heap[smallest]) smallest = l;
            if(r < size && heap[r] < heap[smallest]) smallest = r;

            if(smallest != i){
                swap(i, smallest);
                heapifyDown(smallest);
            }
        }
        private void swap(int i, int j){
            int temp = heap[i];
            heap[i] = heap[j];
            heap[j] = temp;
        }
    }
}