Java 数据结构 - 堆排序

堆是一种满足特定条件的树，即节点的值大于（或小于）其子节点的值。堆排序是一种排序算法，其中我们使用二叉堆对数组的元素进行排序。

算法

Step 1: Create a new node at the end of heap.
Step 2: Assign new value to the node.
Step 3: Compare the value of this child node with its parent.
Step 4: If value of parent is less than child, then swap them.
Step 5: Repeat step 3 & 4 until Heap property holds.

示例

import java.util.Arrays;
import java.util.Scanner;

public class Heapsort {
   public static void heapSort(int[] myArray, int length) {
      int temp;
      int size = length-1;
      
      for (int i = (length / 2); i >= 0; i--) {
         heapify(myArray, i, size);
      }
      for(int i = size; i>=0; i--) {
         temp = myArray[0];
         myArray[0] = myArray[size];
         myArray[size] = temp;
         size--;
         heapify(myArray, 0, size);
      }
	   System.out.println(Arrays.toString(myArray));		   
   }
   public static void heapify (int [] myArray, int i, int heapSize) {
      int a = 2*i;
      int b = 2*i+1;
      int largestElement;
      
      if (a<= heapSize && myArray[a] > myArray[i]) {
         largestElement = a;
      } else {
         largestElement = i;
      }
      if (b <= heapSize && myArray[b] > myArray[largestElement]) {
         largestElement = b;
      }
      if (largestElement != i) {
         int temp = myArray[i];
         myArray[i] = myArray[largestElement];
         myArray[largestElement] = temp;
         heapify(myArray, largestElement, heapSize);
      }
   }	
   public static void main(String args[]) {
      Scanner scanner = new Scanner(System.in);
      System.out.println("Enter the size of the array :: ");
      int size = scanner.nextInt();      
      System.out.println("Enter the elements of the array :: ");
      int[] myArray = new int[size];
      
      for(int i = 0; i<size; i++) {    	  
         myArray[i] = scanner.nextInt();    	  
      }      
      heapSort(myArray, size);	   
   }		
}

输出

Enter the size of the array :: 
5
Enter the elements of the array :: 
45
125
44
78
1
[1, 44, 45, 78, 125]