堆排序，前一个其实写错了

前几天写了一个堆排序，发现其实有个错误。

我写了如下一个代码：

 

private void HeapSort() { int start=0; int end=buffer.Length-1; while (start < end) { AdjustHeap(buffer, start, end); Swap(buffer, start, end);//make the array from start to end as big root heap end--; } } private void AdjustHeap(int[] buffer, int start, int end) { int currentPos = end; int parantPos = (currentPos-1) / 2; while (parantPos >= start) { if (buffer[currentPos] > buffer[parantPos]) Swap(buffer, currentPos, parantPos); currentPos--; parantPos = (currentPos-1) / 2; } } 

 

发现AdjustHeap其实没有整理成大根堆，而是类似于冒泡法把最大一个节点放到了头上。

但是堆调整是不充分的。

 

所以我想到要使用堆排序的话，必须要建立一个树结构，Initialheap的时候是对整个树结构做调整。

这只要做一次。而交换过一次后就可以只对头元素找一个合适他的位子就好了。因为其他的元素已经是堆了。

 

所以貌似很难利用Array中未排的元素作为二叉树，因为随着Array长度减少，叶子节点会有漂移。

就不能保证    “除了头元素以外别的元素仍然是树这个前提”。

 

或者就是每次对前面未排的array当做二叉树做全体initialHeap，如下：

 

但这样感觉是不合算的：

 

using System;using System.Collections.Generic;using System.Text;namespace ACM{ public class HeapSortClass2 { private readonly int[] buffer = { 5, 21, 6, 8, 9, 32, 13, 12, 41, 2, 3, 4, 1 }; public void Run() { HeapSort(); this.PrintAll(); } private void HeapSort() { int start = 0; int end = buffer.Length - 1; InitialHeap(buffer, start, end); while (start < end) { Swap(buffer, start, end);//make the array from start to end as big root heap end--; //AdjustHeap(buffer, start, end); InitialHeap(buffer, start, end); } } private void AdjustHeap(int[] buffer, int start, int end) { int currentPos = start; int switchPos = GetSwitchPos(currentPos, end); while (switchPos != currentPos) { Swap(buffer, currentPos, switchPos); currentPos = switchPos; switchPos = GetSwitchPos(currentPos, end); } } private int GetSwitchPos(int currentPos, int end) { int leftPos = currentPos * 2 + 1; int rightPos = currentPos * 2 + 2; if (rightPos <= end) { if (buffer[rightPos] <= buffer[currentPos] && buffer[leftPos] <= buffer[currentPos]) return currentPos; else if (buffer[leftPos] > buffer[rightPos]) return leftPos; else return rightPos; } else if (leftPos <= end) { if (buffer[leftPos] > buffer[currentPos]) return leftPos; else return currentPos; } else { return currentPos; } } private void InitialHeap(int[] buffer, int start, int end) { int currentPos = end; int parantPos = (currentPos - 1) / 2; while (parantPos >= start) { if (buffer[currentPos] > buffer[parantPos]) AdjustHeap(buffer, parantPos, end); currentPos--; parantPos = (currentPos - 1) / 2; } } private void PrintAll() { for (int i = 0; i < buffer.Length; i++) { Console.Write(buffer[i] + ", "); } } private static void Swap(int[] numbers, int i, int j) { int number = numbers[i]; numbers[i] = numbers[j]; numbers[j] = number; } }}