八大排序算法之-堆排序 java代码

import java.util.Arrays;

/**
* Created by Administrator on 2017/8/2.
*/
public class heapSort_select {
public static void main(String args[]) {
int[] arr = { 6, 9, 1, 3, 1, 2, 2, 5, 6, 1, 3, 5, 9, 7, 2, 5, 6, 1, 9 };
//[1, 1, 1, 1, 2, 2, 2, 3, 3, 5, 5, 5, 6, 6, 6, 7, 9, 9, 9]
heapSort(arr,0,arr.length-1);
System.out.println(Arrays.toString(arr));
}

/*算法思想：
* 大根堆：根部最大，可用于求最小k个数
* 小根堆：根部最小，可用于求最大k个数
*
* 1.首先将序列构建成大根堆
* 2.取出当前最大堆根节点，将其与序列末尾的元素进行交换；
* （此时，序列末尾的值已经是最大值）
* 3.对交换后的n-1个元素进行调整，使其满足大顶堆的性质
* 4.重复2,3直到堆中只有一个元素为止*/

/*时间复杂度：O(nlogn)
* 空间复杂度：*/
private static void heapSort(int[] arr, int start, int end) {
/*if (arr==null || arr.length<=1) {

}*/
for (int i = 0; i<=end; i++) {
heapInsert(arr,arr[i],i);
}
System.out.println(Arrays.toString(arr));

for (int i = end - 1; i>=0; i--) {
swap(arr,0,i+1);
selfBalanceHeap(arr,0,i);
}

}

private static void selfBalanceHeap(int[] heap, int index, int end) {
int left = index * 2 + 1;
int right = index * 2 + 2;
int largest = index;
while (left<=end) {
if ( heap[left]>heap[index]) {
largest = left;
}
if (right<=end && heap[right]>heap[largest]) {//此处应该和heap【largest】进行比较，即最大值，否则会出错
largest = right;
}
if (index!=largest) {
swap(heap,index,largest);
}else {
break;
}
index = largest;
left = index*2 +1;
right = index*2+2;
}

}

private static void heapInsert(int[] heap, int value, int index) {
heap[index] = value;
while (index!=0) {
int parent = (index - 1)/2;
if (heap[parent] <heap[index]) {
swap(heap,parent,index);
index = parent;
}else {
break;
}
}
}

private static void swap(int[] heap, int parent, int index) {
int tmp = heap[parent];
heap[parent] = heap[index];
heap[index] = tmp;
}
}