堆排序

package basic_class_01;

import java.util.Arrays;

```

* 左神源码

* 堆排序的细节和复杂度分析

* 时间复杂度O(N*logN)，额外空间复杂度O(1)

* 堆结构非常重要

1，堆结构的heapInsert与heapify

2，堆结构的增大和减少

3，如果只是建立堆的过程，时间复杂度为O(N)

4，优先级队列结构，就是堆结构

*

*/

public class Code_03_HeapSort {

public static void heapSort(int[] arr) {

if (arr == null || arr.length < 2) {

return;

}

for (int i = 0; i < arr.length; i++) {

heapInsert(arr, i);

}

int size = arr.length;

swap(arr, 0, --size);

while (size > 0) {

heapify(arr, 0, size);

swap(arr, 0, --size);

}

}

//构建大根堆

public static void heapInsert(int[] arr, int index) {

while (arr[index] > arr[(index - 1) / 2]) {

swap(arr, index, (index - 1) / 2);

index = (index - 1) / 2;

}

}

//某位置变化后堆的调整

public static void heapify(int[] arr, int index, int size) {

int left = index * 2 + 1;

while (left < size) {

int largest = left + 1 < size && arr[left + 1] > arr[left] ? left + 1 : left;//取最大的孩子的下标

largest = arr[largest] > arr[index] ? largest : index;

if (largest == index) {

break;

}

swap(arr, largest, index);

index = largest;

left = index * 2 + 1;

}

}

public static void swap(int[] arr, int i, int j) {

int tmp = arr[i];

arr[i] = arr[j];

arr[j] = tmp;

}

// for test

public static void comparator(int[] arr) {

Arrays.sort(arr);

}

// for test

public static int[] generateRandomArray(int maxSize, int maxValue) {

int[] arr = new int[(int) ((maxSize + 1) * Math.random())];

for (int i = 0; i < arr.length; i++) {

arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());

}

return arr;

}

// for test

public static int[] copyArray(int[] arr) {

if (arr == null) {

return null;

}

int[] res = new int[arr.length];

for (int i = 0; i < arr.length; i++) {

res[i] = arr[i];

}

return res;

}

// for test

public static boolean isEqual(int[] arr1, int[] arr2) {

if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {

return false;

}

if (arr1 == null && arr2 == null) {

return true;

}

if (arr1.length != arr2.length) {

return false;

}

for (int i = 0; i < arr1.length; i++) {

if (arr1[i] != arr2[i]) {

return false;

}

}

return true;

}

// for test

public static void printArray(int[] arr) {

if (arr == null) {

return;

}

for (int i = 0; i < arr.length; i++) {

System.out.print(arr[i] + " ");

}

System.out.println();

}

// for test

public static void main(String[] args) {

int testTime = 500000;

int maxSize = 100;

int maxValue = 100;

boolean succeed = true;

for (int i = 0; i < testTime; i++) {

int[] arr1 = generateRandomArray(maxSize, maxValue);

int[] arr2 = copyArray(arr1);

heapSort(arr1);

comparator(arr2);

if (!isEqual(arr1, arr2)) {

succeed = false;

break;

}

}

System.out.println(succeed ? "Nice!" : "Fucking fucked!");

int[] arr = generateRandomArray(maxSize, maxValue);

printArray(arr);

heapSort(arr);

printArray(arr);

}

```