堆排序（java)，

堆排序（java)，

说明：

• 大顶堆
• 待排队列的第一个元素下标为0（要注意与下标为1的不同）

整体过程

注意：写算法时所出现的错误

• 不要把队列的长度(length)与需要建堆的队列的长度（heapLength)混淆:length长度不变，heapLength在堆排序的过程中变小：  heapLength<=length
• 弄清每个循环的开始和结束
    排序循环结束点为要排序队列的剩1个元素还没排序
• 防止在维护堆的属性函数中把递归点设置在判断是否largest等于start之外
  if(largest!=start) {
     exchange(list, start, largest);
     maxMaintainProperty(list, largest,end);//不要写在if语句之外
   }
• 细节必须注意：如果队列第一个元素的下标是0，一定要在维护堆属性函数中得出左孩子（或右孩子）下标不是2*i,而是2*i+1

源码：

 错误的：虽然调试中用的测试数据最终结果没有出现错误

 public class MaxHeapSort { private List<Integer> willHeap=new ArrayList<Integer>(); private int heapLength; public MaxHeapSort(List<Integer> willHeap){ this.willHeap=willHeap; this.heapLength=willHeap.size()-1; } public void sort(){ if(willHeap.size()<2){ return; }else { buildHeap(willHeap); while (heapLength>0) {//不要写为heapLength>-1或1 exchange(willHeap, 0, heapLength); heapLength--; if (heapLength>0) { maxMaintainProperty(willHeap, 0, heapLength); } } } } private void buildHeap(List<Integer> unOrderList){ for (int i = unOrderList.size()/2; i > -1; i--) {//错误:不是 int i = unOrderList.size()/2 maxMaintainProperty(unOrderList, i,unOrderList.size()-1);//attention } } /*** * maintain the property of the max heap * @param list * @param start * @param end */ private void maxMaintainProperty(List<Integer> list,int start,int end){ int largest=0; int left=2*start;//错误 错误 错误，因为起始元素下标为0 int right=left+1; //find the largest element of the father and children if(left<=end&&list.get(start)<list.get(left)){ largest=left; }else { largest=start; } if(right<=end&&list.get(largest)<list.get(right)){ largest=right; } if(largest!=start){ exchange(list, start, largest); maxMaintainProperty(list, largest,end);//注意 } } private List<Integer> exchange(List<Integer> exList,int fElement,int sElement){ int temp=exList.get(fElement); exList.set(fElement, exList.get(sElement)); exList.set(sElement, temp); return exList; } }

 

正确的代码：

public class MaxHeapSort { private List<Integer> willHeap=new ArrayList<Integer>(); private int heapLength; public MaxHeapSort(List<Integer> willHeap){ this.willHeap=willHeap; this.heapLength=willHeap.size()-1; } public void sort(){ if(willHeap.size()<2){ return; }else { buildHeap(willHeap); while (heapLength>0) {//不要写为heapLength>-1或1 exchange(willHeap, 0, heapLength); heapLength--; if (heapLength>0) { maxMaintainProperty(willHeap, 0, heapLength); } } } } private void buildHeap(List<Integer> unOrderList){ for (int i = unOrderList.size()/2-1; i > -1; i--) {//注意 maxMaintainProperty(unOrderList, i,unOrderList.size()-1);//attention } } /*** * maintain the property of the max heap * @param list * @param start * @param end */ private void maxMaintainProperty(List<Integer> list,int start,int end){ int largest=0; int left=2*start+1;//应该是这样 int right=left+1; //find the largest element of the father and children if(left<=end&&list.get(start)<list.get(left)){ largest=left; }else { largest=start; } if(right<=end&&list.get(largest)<list.get(right)){ largest=right; } if(largest!=start){ exchange(list, start, largest); maxMaintainProperty(list, largest,end);//注意 } } private List<Integer> exchange(List<Integer> exList,int fElement,int sElement){ int temp=exList.get(fElement); exList.set(fElement, exList.get(sElement)); exList.set(sElement, temp); return exList; } }