C# 排序算法之堆排序

namespace HeapSort
{
using System;
class Program
{
static int heapSize =0;
static void Main(string[] args)
{
var heap = new[] { -1, 10, 5, 12, 77, 54, 7, 34, 23, 11 };//为了方便，索引0处不存放元素（或存放无用元素）
heapSize = heap.Length - 1;
BuildMaxHeap(heap);
for (var i = heap.Length - 1; i >= 2; i--)
{
//1.每次在构建好最大堆后，将第一个元素和最后一个元素交换；
//2.第一次以索引1到length-1出的元素组成新的堆，第二次1到length-2，直到剩下最后两个元素组成堆
//3.每次新组成的堆除了根节点其他节点都能保持最大堆的特性，因此只要DoBuildMaxHeap(heap, 1)就可以得到新的最大堆
Swap(heap, 1, i);
heapSize--;
MaxHeapfy(heap, 1);
}
foreach (var i in heap)
Console.Write(i + " ");
}
static void BuildMaxHeap(int[] heap)
{
for (var i = (heap.Length - 1) / 2; i >= 1; i--)
{
MaxHeapfy(heap, i);
}
}
static void MaxHeapfy(int[] heap, int index)
{
var largerItemIndex = index;
var leftChildIndex = index << 1;
var rightChildIndex = (index<<1) + 1;
if (leftChildIndex <= heapSize && heap[leftChildIndex] > heap[index])
{
largerItemIndex = leftChildIndex;
}
if (rightChildIndex <= heapSize && heap[rightChildIndex] > heap[largerItemIndex])
{
largerItemIndex = rightChildIndex;
}
if( index != largerItemIndex)
{
Swap(heap, index, largerItemIndex);
MaxHeapfy(heap, largerItemIndex);
}
}
static void Swap(int[] heap, int index1, int index2)
{
var temp = heap[index1];
heap[index1] = heap[index2];
heap[index2] = temp;
}
}
}