归并排序 && 快速排序

 1 #include <cstdio>
 2 int cnt=0;
 3 int x1[50010],x2[50010];
 4 void Merge(int a[],int b[],int left,int middle,int right)
 5 {
 6     int i=left,j=middle+1,k=left;
 7     while(i!=middle+1&&j!=right+1)
 8     {
 9         if(a[i]<=a[j])
10         {
11             b[k++]=a[i++];
12         }
13         else
14         {
15             cnt+=middle-i+1;  //归并排序求逆序数  
16             b[k++]=a[j++];
17         }
18        // printf("%d\n",cnt);
19     }
20     while(i!=middle+1)
21     {
22         b[k++]=a[i++];
23     }
24     while(j!=right+1)
25     {
26         b[k++]=a[j++];
27     }
28     for(int i=left;i<=right;i++)
29     {
30         a[i]=b[i];
31         //printf("%d ",a[i]);
32     }
33     //printf("\n");
34 }
35 
36 void Merge_sort(int a[],int b[],int left,int right)
37 {
38     int middle;
39     if(left<right)
40     {
41         middle=(left+right)/2;
42         //printf("%d %d %d\n",left,right,middle);
43         Merge_sort(a,b,left,middle);
44         Merge_sort(a,b,middle+1,right);
45         Merge(a,b,left,middle,right);
46     }
47     return;
48 }
49 
50 int main()
51 {
52    // freopen("a.txt","r",stdin);
53     int n;
54     scanf("%d",&n);
55     for(int i=0;i<n;i++)
56     {
57         scanf("%d",&x1[i]);
58     }
59     Merge_sort(x1,x2,0,n-1);
60     printf("%d\n",cnt);
61     return 0;
62 }

 1 #include <cstdio>
 2 
 3 void qsort(int a[],int left,int right)
 4 {
 5     if(left>=right)  //完成一次 排序
 6     {
 7         return;
 8     }
 9     int key=a[left],i=left,j=right;
10     while(i<j)
11     {
12         while(i<j&&key<=a[j])
13         {   //从后往前查找 比key小的数丢到前面去
14             j--;
15         }
16         a[i]=a[j];
17         while(i<j&&key>=a[i])
18         {   //从前往后查找 比key大的数丢到后面去
19             i++;
20         }
21         a[j]=a[i];
22     }
23     a[i]=key;  //在key左边的都比key小，右边的都比key大
24     qsort(a,left,i-1); //继续递归 直到 剩下一个数
25     qsort(a,i+1,right);
26 }
27 int main()
28 {
29     int a[8]={23,10,34,5,9,39,84,77};
30     qsort(a,0,7);
31     for(int i=0;i<8;i++)
32         printf("%d\n",a[i]);
33     return 0;
34 }