堆排序

堆排序

import edu.princeton.cs.algs4.StdOut;
public class HeapSort {
public static void sort(Comparable[] a){
int N = a.length;
for(int k = N/2; k>=1; k--)         //堆的构造，自底向上狗造，从有子节点的最大节点开始
sink(a, k, N);
while(N > 1){
exch(a, 1, N--);                //将最大的元素与最后一位元素交换，将N减一，下面的排序不会再用到它
sink(a, 1, N);                  //交换后又肯能改变了序列，所以要将堆再次有序化
}
}

private static void exch(Comparable[] a, int i, int j) {
// TODO Auto-generated method stub
Comparable t = a[i];
a[i] = a[j];
a[j] = t;
}

private static void sink(Comparable[] a, int k, int N) {
// TODO Auto-generated method stub
while(2*k<=N){
int j = 2*k;
if(j<N && less(a,j,j+1))
j++;
if(less(a,k,j))
break;
exch(a,k,j);
k = j;
}
}

public static void show(Comparable[] a) {
// TODO Auto-generated method stub
for(int i = 0; i <a.length;i++ )
StdOut.print(a[i] + " ");
StdOut.println();
}
private static boolean less(Comparable[] a,int k, int j) {
// TODO Auto-generated method stub
return a[k].compareTo(j)<0;
}
}