优先队列

一、基于堆的优先队列：

public class MaxPQ<Key extends Comparable<Key>>
{
	private int N = 0;
	private Key[] pq;
	
	public MaxPQ(int maxN)
	{
		pq = (Key[])new Comparable[maxN+1];
	}
	
	public boolean isEmpty()
	{
		return N == 0;
	}
	public int size()
	{
		return N;
	}
	public void insert(Key v)
	{
		pq[++N] = v;
		swim(N);
	}
	public Key delMax()
	{
		Key max = pq[1];
		exch(1, N--);
		pq[N + 1] = null;
		sink(1);
		return max;
	}
	private boolean less(int i, int j)
	{
		return pq[i].compareTo(pq[j]) < 0;
	}
	private void exch(int i, int j)
	{
		Key t = pq[i];
		pq[i] = pq[j];
		pq[j] = t;
		return;
	}
	private void swim(int k)
	{
		while (k > 1 && less(k/2,k))
		{
			exch(k, k/2);
			k = k/2;
		}
	}
	private void sink(int k)
	{
		while (2*k <= N)
		{
			int j = 2 * k;
			if (j < N && less(j, j + 1)) j++;
			if (!less(k, j)) break;
			exch(k,j);
			k = j;
		}
	}
}