Note of introduction of Algorithms (Lecture 1)

This is the note for introduction of Algorithms, based on the MIT open class. The lecture 1 focus on how to measured the performance of program, and two sort algorithms has been mentioned, which is insertion sort and merging sort.

Here is the c program I wrote.I wish it could be a nice start, and whole open classes could been finished in 2013 finnally.

insertion sort

 

View Code

 1 /*

 2  *    Insertion sort

 3  *  written by Fredric

 4  *  2013-5-5

 5  */

 6 #include <stdio.h>

 7 #include <stdlib.h>

 8 

 9 #define        INPUT_LEN    6

10 unsigned int g_input[INPUT_LEN]

11 = {8,2,4,9,3,6};

12 

13 /*

14  *    show function, only for checking the result

15  */

16 void show_permutation(){

17     for (int i = 0; i < INPUT_LEN; i++)

18     {

19         printf("%d", g_input[i]);

20     }

21     printf("\t\n");

22 }

23 

24 /*

25  *  *pinput: pointer of the input array

26  *  len    : the length of input array

27  */

28 void insertion_sort(unsigned int *pintput, int len){

29     unsigned int key = 0;

30     unsigned int tmp = 0;

31     int i = 0;

32 

33     for (int j = 1; j < len; j++)

34     {

35         key = *(pintput+j);

36         i = j - 1;

37         while ((i >= 0)&(*(pintput + i) > key))

38         {

39             //insert the key value

40             tmp = *(pintput + i);

41             *(pintput + i) = *(pintput + i + 1);

42             *(pintput + i + 1) = tmp;

43             

44             

45             i = i - 1;

46         }

47     }

48 }

49 

50 void main(void){

51     

52     insertion_sort(g_input, INPUT_LEN);

53 

54     show_permutation();

55 

56     system("pause");

57 

58     return;

59 }

 

Merging sort

View Code

 1 /*

 2 *  from   : the beginning of the array

 3 *  to     : the end of the array

 4 *  len    : the length of input array

 5 */

 6 void merging_sort(int from, int to){

 7     int i,j,p = 0;

 8 

 9     if (from < to)

10     {

11         int mid = (from + to)/2;

12         

13         //recursively sort

14         merging_sort(from, mid);

15         merging_sort(mid + 1, to);

16 

17         //merge 

18         i = from;

19         j = mid + 1;

20         p = from;

21         while ((i <= mid) || (j <= to))

22         {

23             if (i > mid)

24             {

25                 g_output[p] = g_input[j];

26                 j++;

27                 p++;

28             } 

29             else if (j > to)

30             {

31                 g_output[p] = g_input[i];

32                 i++;

33                 p++;

34             }else{

35                 if (g_input[i] < g_input[j])

36                 {

37                     g_output[p] = g_input[i];

38                     i++;

39                     p++;

40                 } 

41                 else

42                 {

43                     g_output[p] = g_input[j];

44                     j++;

45                     p++;

46                 }

47             }

48         }//end of while

49         

50         for (int t = from; t <= to; t++)

51         {

52             g_input[t] = g_output[t];

53         }

54     }

55 

56     return;

57 }