java编程实现优先队列的二叉堆代码分享

package practice;import edu.princeton.cs.algs4.StdRandom;public class TestMain {  public static void main(String[] args) {    int[] a = new int[20];    for (int i = 0; i < a.length; i++) {      int temp = (int)(StdRandom.random()*100);      a[i] = temp;    }    for (int i : a) {      System.out.print(i+" ");    }    System.out.println();    PQHeap pq = new PQHeap();    for (int i = 0; i < 20; i++) {      pq.insert(a[i]);    }    System.out.println();    for (int i = 0; i < 20; i++) {      System.out.print(pq.delMax()+" ");    }  }}/* * 优先队列的堆实现 * 二叉堆，每个元素有两个子元素，两个子元素均比自己小 */class PQHeap{  private int[] a;  private int p = 1;  public PQHeap() {    a = new int[2];  }  /*   * 插入元素   */  public void insert(int elements) {    if (p == a.length) { resize(a.length*2); }    a[p++] = elements;    swim(p - 1); //将刚插入的元素上浮到正确位置  }  /*   * 返回并删除最大元素   */  public int delMax() {    if (p == a.length/4) { resize(a.length/2); }    int result = a[1]; //找出最大元素    exch(1, --p); //将最后一个元素移到顶端    a[p] = 0;     sink(1); //将刚移上去的元素沉下去，使堆有序    return result;  }  public boolean isEmpty() {    return p == 0;  }  public int size() {    return p;  }  public void show() {    for (int i : a) {      System.out.print(i+" ");    }    System.out.println();  }  /*   * 上浮元素   */  private void swim(int k) { //将元素与父元素比较，比父元素大则换位置    while (k > 1 && a[k/2] < a[k]) {       exch(k/2, k);      k = k/2;    }  }  private void sink(int k) { //将元素与子元素比较，比子元素小则和两个中较大的那个换位置    while (2*k < p && (a[k] < a[2*k + 1]) || (a[k] < a[2*k])) {      if (a[2*k + 1] > a[2*k]) { exch(k, 2*k + 1); k = 2*k + 1; }      else           { exch(k, 2*k); k = 2*k; }    }  }  private void resize(int length) {    int[] b = new int[length]; //将数组长度改变    for (int i = 0; i < p; i++) { //将数组复制      b[i] = a[i];    }    a = b; //让a指向b的内存空间  }  /*   * 交换   */  private void exch (int i, int j) {    int t = a[i];    a[i] = a[j];    a[j] = t;  }}