Merge Sort

作者：jostree 转载请注明出处 http://www.cnblogs.com/jostree/p/4030019.html

算法导论第二章的归并排序，注意在merge步骤时，要开辟临时数组保存两个数组排序候的结果，然后在把临时数组逐个导入待排序数组中。

代码如下：

 1 #include <cstdio>

 2 #include <iostream>

 3 #include <vector>

 4 using namespace std;

 5 void merge(vector<int> &arr, int s1, int e1,  int e2)

 6 {

 7     int p1 = s1;

 8     int p2 = e1+1;

 9     vector<int> tmp;

10     while( p1 <= e1 && p2 <= e2 )

11     {

12         if( arr[p1] < arr[p2] )

13         {

14             tmp.push_back(arr[p1]);

15             p1++;

16         }

17         else

18         {

19             tmp.push_back(arr[p2]);

20             p2++;

21         }

22     }

23     while( p2 <= e2 )

24     {

25         tmp.push_back(arr[p2]);

26         p2++;

27     }

28     while(p1 <= e1)

29     {

30         tmp.push_back(arr[p1]);

31         p1++;

32     }

33     int j = 0;

34     for( int i = s1 ; i <= e2 ; i++ )

35     {

36         arr[i] = tmp[j++];

37     }

38 }

39 

40 void mergesort(vector<int> &arr, int s, int e)

41 {

42     if( s < e )

43     {

44         int mid = (s+e)/2;

45         mergesort(arr, s, mid);

46         mergesort(arr, mid+1,e);

47         merge(arr, s, mid, e);

48     }

49 }

50 

51 int main(int argc, char *argv[])

52 {

53     vector<int> a; 

54     int n;

55     cin>>n;

56     for( int i = 0 ; i < n ;i++  )

57     {

58         int tmp;

59         cin>>tmp;

60         a.push_back(tmp);

61     }

62     mergesort(a, 0, n-1);

63     for( int i = 0 ; i < n ; i++ )

64     {

65         cout<<a[i]<<" ";

66     }

67     cout<<endl;

68 }

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