堆排序及其分析

實作算法:

private static int leftChild(int i){

return 2*i+1;

}

private static <AnyType extends Comparable<? super AnyType>> void percDown(AnyType[] a,int i,int n){

int child;

AnyType tmp;

for(tmp=a[i];leftChild(i)<n;i=child){

child = leftChild(i);

if(child != (n-1)&&a[child].compareTo(a[child+1])<0)

child++;

if(tmp.compareTo(a[child])<0)

a[i]=a[child];

else

break;

}

a[i]=tmp;

}

public static <AnyType extends Comparable<? super AnyType>> void heapsort(AnyType[] a){

for(int i=a.length/2;i>=0;i--)//buildHeap

percDown(a,i,a.length);

for(int i=a.length-1;i>0;i--){

swapReferences(a,0,i);//deleteMax

percDown(a,0,i);

}

}

堆排序總是使用至少NlogN-O(N)次比較，輸入資料可以達到這個值

平均比較次數為2NlogN-O(N)