171 lines
4.2 KiB
Java
171 lines
4.2 KiB
Java
/**
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* File: my_heap.java
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* Created Time: 2023-01-07
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* Author: Krahets (krahets@163.com)
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*/
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package chapter_heap;
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import include.*;
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import java.util.*;
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class MaxHeap {
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// 使用列表而非数组，这样无需考虑扩容问题
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private List<Integer> maxHeap;
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/* 构造函数，建立空堆 */
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public MaxHeap() {
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maxHeap = new ArrayList<>();
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}
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/* 构造函数，堆化 nums 所有元素 */
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public MaxHeap(List<Integer> nums) {
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// 将元素拷贝至堆中
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maxHeap = new ArrayList<>(nums);
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// 堆化除叶结点以外的其他所有结点
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for (int i = parent(size() - 1); i >= 0; i--) {
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heapify(i);
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}
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}
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/* 获取左子结点索引 */
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private int left(int i) {
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return 2 * i + 1;
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}
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/* 获取右子结点索引 */
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private int right(int i) {
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return 2 * i + 2;
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}
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/* 获取父结点索引 */
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private int parent(int i) {
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return (i - 1) / 2;
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}
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/* 交换元素 */
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private void swap(int i, int j) {
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int a = maxHeap.get(i),
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b = maxHeap.get(j),
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tmp = a;
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maxHeap.set(i, b);
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maxHeap.set(j, tmp);
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}
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/* 获取堆大小 */
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public int size() {
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return maxHeap.size();
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}
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/* 判断堆是否为空 */
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public boolean isEmpty() {
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return size() == 0;
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}
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/* 访问堆顶元素 */
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public int peek() {
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return maxHeap.get(0);
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}
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/* 元素入堆 */
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public void push(int val) {
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// 添加结点
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maxHeap.add(val);
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// 从底至顶堆化
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int i = size() - 1;
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while (true) {
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int p = parent(i);
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if (p < 0 || maxHeap.get(i) <= maxHeap.get(p))
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break;
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swap(i, p);
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i = p;
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}
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}
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/* 元素出堆 */
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public int poll() {
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// 判空处理
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if (isEmpty())
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throw new EmptyStackException();
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// 交换根结点与右下角（即最后一个）结点
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swap(0, size() - 1);
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// 删除结点
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int val = maxHeap.remove(size() - 1);
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// 从顶至底堆化
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heapify(0);
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// 返回堆顶元素
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return val;
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}
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/* 从结点 i 开始，从顶至底堆化 */
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private void heapify(int i) {
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while (true) {
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// 判断结点 i, l, r 中值最大的结点，记为 ma ；
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int l = left(i), r = right(i), ma = i;
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if (l < size() && maxHeap.get(l) > maxHeap.get(ma)) ma = l;
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if (r < size() && maxHeap.get(r) > maxHeap.get(ma)) ma = r;
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// 若结点 i 最大，则无需继续堆化，跳出
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if (ma == i) break;
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// 交换结点 i 与结点 max
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swap(i, ma);
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// 循环向下堆化
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i = ma;
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}
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}
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/* 打印堆（二叉树） */
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public void print() {
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Queue<Integer> queue = new PriorityQueue<>((a, b) -> { return b - a; });
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queue.addAll(maxHeap);
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PrintUtil.printHeap(queue);
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}
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}
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public class my_heap {
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public static void testPush(MaxHeap maxHeap, int val) {
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// 元素入堆
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maxHeap.push(val);
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System.out.format("\n添加元素 %d 后\n", val);
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maxHeap.print();
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}
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public static void testPoll(MaxHeap maxHeap) {
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// 元素出堆
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int val = maxHeap.poll();
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System.out.format("\n出堆元素为 %d\n", val);
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maxHeap.print();
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}
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public static void main(String[] args) {
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/* 初始化堆 */
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// 初始化最大堆
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MaxHeap maxHeap = new MaxHeap();
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/* 元素入堆 */
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testPush(maxHeap, 1);
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testPush(maxHeap, 3);
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testPush(maxHeap, 2);
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testPush(maxHeap, 5);
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testPush(maxHeap, 4);
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/* 获取堆顶元素 */
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int peek = maxHeap.peek();
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System.out.format("\n堆顶元素为 %d\n", peek);
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/* 元素出堆 */
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testPoll(maxHeap);
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testPoll(maxHeap);
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/* 获取堆大小 */
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int size = maxHeap.size();
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System.out.format("\n堆元素数量为 %d\n", size);
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/* 判断堆是否为空 */
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boolean isEmpty = maxHeap.isEmpty();
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System.out.format("\n堆是否为空 %b\n", isEmpty);
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}
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}
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