107 lines
3.1 KiB
Java
107 lines
3.1 KiB
Java
/*
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* The MIT License (MIT)
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*
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* Copyright © 2020 xrv <xrg@live.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package io.github.ehlxr.algorithm.binarytree.heap;
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import java.util.Arrays;
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/**
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* @author ehlxr
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* @since 2022-03-15 07:40.
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*/
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public class Heap {
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private static void createHeap(int[] a) {
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int n = a.length - 1; // 最后一个叶子节点下标
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buildHeap(a, n);
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}
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private static void buildHeap(int[] a, int n) {
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// (n - 1) / 2 表示最后一个叶子节点父节点，即为最后一个非叶子节点
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for (int i = (n - 1) / 2; i >= 0; --i) {
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heapify(a, n, i);
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}
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}
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/**
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* 堆化
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*
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* @param a 数组
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* @param n 最后一个元素下标
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* @param i 需要调整的父节点下标
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*/
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private static void heapify(int[] a, int n, int i) {
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while (true) {
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int max = i;
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// 从当前节点和左右叶子节点中找出最大的
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int l = 2 * i + 1;
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if (l <= n && a[l] > a[max]) {
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max = l;
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}
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int r = 2 * i + 2;
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if (r <= n && a[r] > a[max]) {
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max = r;
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}
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// 当前节点最大时退出
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if (max == i) {
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break;
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}
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swap(a, i, max);
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// 最大节点和当前节点交换后，继续以当前节点为父节点堆化
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i = max;
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}
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}
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/**
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* 堆排序
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*/
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private static void sort(int[] a) {
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for (int i = a.length - 1; i > 0; i--) {
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buildHeap(a, i);
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// 堆顶元素和最后一个元素交换，除过最后一个元素外其它元素再次构建大顶堆
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swap(a, 0, i);
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}
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}
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public static void main(String[] args) {
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int[] arr = new int[]{1, 2, 3, 4, 5, 6};
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createHeap(arr);
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System.out.println(Arrays.toString(arr));
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sort(arr);
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System.out.println(Arrays.toString(arr));
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}
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private static void swap(int[] arr, int i, int j) {
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int tmp = arr[i];
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arr[i] = arr[j];
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arr[j] = tmp;
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}
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}
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