heap.java

package lecture9a22;

import java.util.ArrayList;

public class heap {
	ArrayList<Integer> data = new ArrayList<>();

	public int size() {
		return this.data.size();
	}
//O(log(n))
	public void add(int item) {
		this.data.add(item);
		upheapify(this.size() - 1);
	}

	private void upheapify(int ci) {
		int pi = (ci - 1) / 2;
		if (this.data.get(pi) > this.data.get(ci)) {
			swap(ci, pi);
			upheapify(pi);
		}
	}

	private void swap(int i, int j) {
		int ith = this.data.get(i);
		int jth = this.data.get(j);
		this.data.set(i, jth);
		this.data.set(j, ith);
	}
// O( LOG(N))
	public int remove() {
		swap(0, this.size() - 1);
		int rv = this.data.remove(this.size() - 1);
		downheapify(0);
		return rv;
	}

	private void downheapify(int pi) {
		int lci = 2 * pi + 1;
		int rci = 2 * pi + 2;
		int mini = pi;
		if (lci < this.data.size() && this.data.get(lci) < this.data.get(mini)) {
			mini = lci;
		}
		if (rci < this.data.size() && this.data.get(rci) < this.data.get(mini)) {
			mini = rci;
		}
		if (mini != pi) {
			swap(mini, pi);
			downheapify(mini);
		}

	}
  public void display() {
	  System.out.println(this.data);
  }
  //O(1)
  public int getHP() {
	  return this.data.get(0);
  }
  public boolean isEmpty() {
	  return this.data.size()==0;
  }
}