Algorithmic Implementation series(6) Implementation of Quick_Sort

Compiler: gcc 4.7.3

C++ Standard: C++0x

OS:CentOS 6.3 x86

1 #include <iostream>

2

3 using namespace std;

4

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

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

7 if(i == j) { return; }

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

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

10 ia[j - 1] = tmp;

11 }

12

13 const size_t partition(int ia[], const size_t p,const size_t r) {

14 //The value of variable x is the last element in array ia.

15 const int x = ia[r - 1];

16

17 //Variable i marks the position before the first element in

18 //array ia.

19 int i = p - 2;

20

21 //The for loop goes from the first element inclusive to one

22 //before the last element in array ia.

23 for(size_t j = p; j != r; ++j) {

24 if(ia[j - 1] <= x) {

25 ++i;

26 swap_elements(ia, i + 1, j);

27 }

28 }

29 swap_elements(ia, i + 2, r);

30 return i + 2;

31 }

32

33 void Quick_Sort(int ia[], const size_t p,const size_t r) {

34 if(p < r) {

35 const size_t q = partition(ia, p, r);

36 Quick_Sort(ia, p, q - 1);

37 Quick_Sort(ia, q + 1, r);

38 }

39 }

40

41 int main() {

42 int ia[] = {2, 32, 4, 6, -2, 4, 5, -55, -3, 55, 88};

43 const size_t size = sizeof(ia)/sizeof(int);

44

45 Quick_Sort(ia, 1, size);

46

47 for(size_t i = 0; i != size; ++i) {

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

49 }

50 cout << endl;

51

52 return EXIT_SUCCESS;

53 }

54