算法实现-堆排序
package com.sort;
public class HeapSort {
/**
* 将整棵树构建为最大堆
* @param a
*/
public void builMaxHeap(int[] a){
int length = a.length-1;//堆排序数据长度,第一个数据不使用,设置为0,哨兵值
int heapSize = length/2;
for(;heapSize > 0 ;heapSize--){
maxHeapfy(a,heapSize);
}
}
/**
* 将子树构建为最大堆
* @param a
* @param root
*/
public void maxHeapfy(int[] a,int root){
int largest = root;
int left = 2*largest;
int right = 2*largest +1;
if(left>a.length-1){//当左子树大于数组最后一个元素的下标时,直接返回
return;
}else if(left == a.length-1){//当左子树等于数组最后一个元素的下标时,比较数组
if(a[root]<a[left]){
int tmp = a[root];
a[root] = a[left];
a[left]= tmp;
}
return;
}
//其他情况则表示存在右节点,按照一颗完整子树去比较根节点与左右子树的大小
if(a[largest]<a[left]){
largest = left;
}
if(a[largest]<a[right]){
largest = right;
}
if(root != largest){//保持树中的根节点为最大值
int tmp;
tmp = a[root];
a[root] = a[largest];
a[largest] = tmp;
}else if(root == largest){//如果根节点为最大值
if(a[left]>a[right]){//比较左右子树的大小
largest = left;
}else{
largest = right;
}
}
//largest = largest + 1;
maxHeapfy(a,largest);
}
/**
* 堆排序算法
* @param a
* @return
*/
public int[] heapSort(int[] a){
this.builMaxHeap(a);
int length = a.length-1;
int[] b = new int[a.length];
b[0] = -1;//哨兵值,这个树不参与排序,和a数组中第一个值保持一致
for(int i=length;i>0;i--){//循环将树重新构建成最大堆
b[i] = a[1];//将新构建的最大堆中根节点赋值给数组b
a[1] = -1;//将根节点赋值无用的-1标记
this.maxHeapfy(a, 1);//重新构建堆
}
return b;
}
public static void main(String[] args) {
int[] a = new int[]{-1,4,1,3,2,16,22,23,0,25,25,25,9,10,14,8,1000};
HeapSort heapSort = new HeapSort();
int[] b = heapSort.heapSort(a);
for(Integer sortHeap:b){
System.out.println(sortHeap);
}
}
}