堆排序——算法系列

堆排序：

堆排序的思想，建立一个最大最小堆，通过不断取出堆顶的值，重建堆，再取出，得到排序。

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Net;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 1; i <= 5; i++)
            {
                List<int> list = new List<int>();
                //插入2k个随机数到数组中
                for (int j = 0; j < 2000; j++)
                {
                    Thread.Sleep(1);
                    list.Add(new Random((int)DateTime.Now.Ticks).Next(0, 100000));
                }
                Console.WriteLine("\n第" + i + "次比较：");
                Stopwatch watch = new Stopwatch();
                watch.Start();
                var result = list.OrderBy(single => single).ToList();//这里这个single=>single不懂
                watch.Stop();
                Console.WriteLine("\n系统的快速排序耗费时间：" + watch.ElapsedMilliseconds);
                Console.WriteLine("输出前是十个数："+string.Join(",",result.Take(10).ToList()));
                watch.Start();
                result = HeapSort(list);
                watch.Stop();
                Console.WriteLine("\n堆排序耗费时间：" + watch.ElapsedMilliseconds);
                Console.WriteLine("输出前是十个数：" + string.Join(",", result.Take(10).ToList()));
                
            }
            
            Console.ReadLine();
        }
        //堆排序算法
        static void HeapAdjust(List<int> list, int parent, int length)
        {
            int temp = list[parent];
            int child = 2 * parent + 1;
            while (child < length)
            {
                if (child + 1 < length && list[child] < list[child + 1])
                    child++;
                if (temp > list[child])
                    break;
                list[parent] = list[child];
                parent = child;
                child = 2 * parent + 1;
            }
            list[parent] = temp;
        }

        public static List<int> HeapSort(List<int> list)
        {
            for (int i = list.Count / 2 - 1; i >= 0; i--)
            {
                HeapAdjust(list, i, list.Count);
            }

            for (int i = list.Count - 1; i >= 0; i--)
            {
                int temp = list[0];
                list[0] = list[i];
                list[i] = temp;
                HeapAdjust(list, 0, i);
            }
            return list;
        }
    }
}

总结：堆排序一般的操作步骤就不说了，这里有一点要注意的就是，初始建堆的时候，是从叶子节点开始调整，一直到根，这样才能得到正确的堆。