算法导论：堆排序

 1 //goal: heap sort
 2 //time: 9/7/2014
 3 //author: zrss
 4 //reference: introduction to algorithms
 5 
 6 #include <cstdio>
 7 #include <cstring>
 8 
 9 #define MAX_DATA 10
10 
11 class MaxHeap {
12 public:
13     MaxHeap(int *data, int size);
14 
15     void heap_sort(void); //堆排序，升序
16 
17     void output(void);
18 
19 private:
20     void max_heapify(int i, int size); //使以i为根的子树成为最大堆，假设i左右子树均为最大堆
21     void build_maxheap(int size); //自底向上使用max_heapify调整，建堆
22 
23 private:
24     int size;
25     int array[MAX_DATA]; //从下标0开始存储
26 };
27 
28 MaxHeap::MaxHeap(int *data, int size):size(size) {
29     if (size > MAX_DATA)
30         return;
31 
32     memcpy(array, data, sizeof(int) * size);
33 }
34 
35 void MaxHeap::max_heapify(int i, int size) {
36     bool check = true;
37 
38     while (check) {
39         int l = (i << 1) + 1;
40         int r = l + 1;
41 
42         int largest = i;
43 
44         //与子节点比较
45         if (l < size && array[l] > array[i])
46             largest = l;
47 
48         if (r < size && array[r] > array[largest])
49             largest = r;
50 
51         if (largest != i) {
52             int temp = array[largest];
53             array[largest] = array[i];
54             array[i] = temp;
55 
56             i = largest; //从被交换的子节点位置继续调整
57         }
58         else
59             check = false; //父节点不小于子节点，满足最大堆性质，停止调整
60     }
61 }
62 
63 void MaxHeap::build_maxheap(int size) {
64     int leaf_start_index = size >> 1; //后续元素为叶子节点
65 
66     //从第一个父节点开始调整
67     for (int i = leaf_start_index - 1; i >= 0; --i)
68         max_heapify(i, size);
69 }
70 
71 void MaxHeap::heap_sort(void) {
72     int cur_size = size;
73 
74     while (cur_size > 1) {
75         //调整成堆
76         build_maxheap(cur_size);
77 
78         //将最大值与堆末尾元素交换
79         int temp = array[cur_size - 1];
80         array[cur_size - 1] = array[0];
81         array[0] = temp;
82 
83         --cur_size;
84     }
85 }
86 
87 void MaxHeap::output(void) {
88     for (int i = 0; i < size; ++i)
89         printf("%d ", array[i]);
90 }