Algorithmic Implementation series(5) Implementation of Heap_Sort

compiler: gcc 4.7.3

C++0X

OS: centos 6.3 x86

1 #include <iostream>

2

3 using namespace std;

4

5 //Getting the subscript of the left child of element i

6 const size_t left(const size_t i) {

7 return i * 2;

8 }

9

10 //Getting the subscript of the right child of element i

11 const size_t right(const size_t i) {

12 return i * 2 + 1;

13 }

14

15 //Getting the subscript of the parent of element i

16 const size_t parent(const size_t i) {

17 return i / 2;

18 }

19

20 //swap the ith element and the jth element in an array

21 void swap_elements(int ia[], const size_t i, const size_t j) {

22 const int tmp = ia[i - 1];

23 ia[i - 1] = ia[j - 1];

24 ia[j - 1] = tmp;

25 }

26

27 void Max_Heapify(int ia[], const size_t i,

28 const size_t heap_size) {

29 const size_t l = left(i);

30 const size_t r = right(i);

31

32 //Storing the subscript of the one among element i and its left

33 //and right child, the value of which is the largest.

34 size_t largest = i;

35

36 if(l <= heap_size && ia[l - 1] > ia[i - 1]) {

37 largest = l;

38 }

39

40 if(r <= heap_size && ia[r -1] > ia[largest -1]) {

41 largest = r;

42 }

43

44 if(largest != i) {

45 swap_elements(ia, i, largest);

46 Max_Heapify(ia, largest, heap_size);

47 }

48 }

49

50 void Build_Max_Heap(int ia[], const size_t size) {

51 const size_t heap_size = size;

52 for(size_t i = size / 2; i != 0; --i) {

53 Max_Heapify(ia, i, heap_size);

54 }

55 }

56

57 void Heap_Sort(int ia[], const size_t size) {

58 Build_Max_Heap(ia, size);

59

60 size_t heap_size = size;

61

62 for(size_t i = size; i > 1; --i) {

63 swap_elements(ia, 1, i);

64 --heap_size;

65 Max_Heapify(ia, 1, heap_size);

66 }

67 }

68

69

70 int main() {

71 int ia[] = {3, 2, 4, -3, -22, 12, 43, -55, 66, -65, 99};

72 int *pa = &ia[0];

73

74 Heap_Sort(pa, sizeof(ia)/sizeof(int));

75

76 for(size_t i = 0; i != sizeof(ia)/sizeof(int); ++i) {

77 cout << ia[i] << " ";

78 }

79 cout << endl;

80

81 return EXIT_SUCCESS;

82 }