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HeapSort.java
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68 lines (62 loc) · 1.87 KB
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import java.util.Arrays;
/**
* @program JavaBooks
* @description: 堆排序
* @author: mf
* @create: 2019/08/14 15:24
*/
/*
- 创建一个堆 H[0……n-1]；
- 创建一个大根堆
- 堆顶和堆尾交换
- 重复第三步骤
*/
public class HeapSort {
public static void main(String[] args) {
int[] arr = {3, 5, 1 , 4, 2};
System.out.println("Heap Sort...");
System.out.println(Arrays.toString(arr));
heapSort(arr);
System.out.println(Arrays.toString(arr));
}
public static void heapSort(int[] arr) {
if (arr == null || arr.length < 2) return;
for (int i = 0; i < arr.length; i++) {
heapInsert(arr, i); // 依次从0～i形成大根堆
}
int heapSize = arr.length;
swap(arr, 0, --heapSize);
while (heapSize > 0) {
heapify(arr, 0, heapSize);
swap(arr, 0, --heapSize);
}
}
public static void heapInsert(int[] arr, int index) {
// 建立大根堆
while (arr[index] > arr[(index - 1) / 2]) {
swap(arr, index, (index - 1) / 2);
index = (index - 1) / 2;
}
}
public static void swap(int[] arr, int i, int j) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
public static void heapify(int[] arr, int index, int heapSize) {
// 调整成大根堆
int left = index * 2 + 1;
while (left < heapSize) {
int largest = left + 1 < heapSize && arr[left + 1] > arr[left]
? left + 1
: left;
largest = arr[largest] > arr[index] ? largest : index;
if (largest == index) {
break; // 自己已经是最大了， 直接跳出
}
swap(arr, largest, index);
index = largest;
left = index * 2 + 1;
}
}
}