数据结构与算法——排序算法

 1 package day20140520;
 2 
 3 import java.util.ArrayList;
 4 import java.util.LinkedList;
 5 import java.util.Scanner;
 6 
 7 public class HeapSorting {
 8 
 9     /**
10      * 创建最大堆
11      * @param a
12      * @param i
13      */
14     private static void buildMaxHeap(ArrayList<Integer> a, int i) {
15         if(i < 0)
16             return;
17         int l = 2 * i + 1;
18         int r = 2 * i + 2;        
19         if (l < a.size()) {            
20             if (r < a.size()) {
21                 int max = Math.max(a.get(l), a.get(r));
22                 if (max > a.get(i)) {
23                     if (a.get(l) == max) {
24                         a.set(l, a.get(i));
25                         a.set(i, max);
26                         buildMaxHeap(a, l);
27                     } else {
28                         a.set(r, a.get(i));
29                         a.set(i, max);
30                         buildMaxHeap(a, r);
31                     }
32                 } else {
33                     buildMaxHeap(a, --i);
34                 }
35 
36             } else {
37                 if (a.get(i) < a.get(l)) {
38                     int temp = a.get(i);
39                     a.set(i, a.get(l));
40                     a.set(l, temp);
41                     buildMaxHeap(a, l);
42                 } else {
43                     buildMaxHeap(a, --i);
44                 }
45             }
46         } else {
47             --i;
48             buildMaxHeap(a, i);
49         }
50     }
51     
52     /**
53      * 堆排序
54      * @param input
55      */
56     private static LinkedList<Integer> heapSort(ArrayList<Integer> input){
57         LinkedList<Integer> list = null;
58         if(input != null){
59             list = new LinkedList<Integer>();
60         }
61         while(input.size() > 0){
62             int startIndex = input.size() / 2 - 1;
63             buildMaxHeap(input, startIndex);  //构建最大堆
64             //交换堆中第一个和最后一个元素
65             int lastIndex = input.size() - 1;
66             int temp = input.get(lastIndex);
67             input.set(lastIndex, input.get(0));
68             input.set(0, temp);
69             //截取堆中的最后一个元素
70             list.addFirst(input.remove(lastIndex));
71         }            
72         return list;
73     }
74 
75     public static void main(String[] args) {
76         
77         //4 1 3 2 16 9 10 14 8 7
78         Scanner sc = new Scanner(System.in);
79         String in_str = sc.nextLine().trim().replaceAll(" +", " ");
80         String[] in_str_arr = in_str.split(" ");
81         ArrayList<Integer> input = new ArrayList<Integer>();
82         for (int i = 0; i < in_str_arr.length; i++) {
83             input.add(Integer.parseInt(in_str_arr[i]));
84         }
85 
86         LinkedList<Integer> list = HeapSorting.heapSort(input);
87         if(list != null)
88             System.out.println(list);
89     }
90 }