poj 2299 Ultra-QuickSort

归并排序模版：
 1 #include<stdio.h>
 2 
 3 long long int ans, n;
 4 long long int a[501000], b[501000];
 5 
 6 void mergesort(int start, int end)
 7 {
 8     if(start < end)
 9     {
10         int i, j, mid = (start+end)>>1;
11         mergesort(start, mid);
12         mergesort(mid+1, end);
13         int t = start;
14         j = mid+1; i = start;
15         while(i<=mid && j <= end)
16         {
17             if(a[i] <= a[j])
18                 b[t++] = a[i++];
19             else
20             {
21                 b[t++] = a[j++];
22                 ans += mid-i+1;
23             }
24         }
25         while(i<=mid)
26             b[t++] = a[i++];
27         while(j<=end)
28             b[t++] = a[j++];
29         for(int k = start; k <= end; k ++)
30         a[k] = b[k];
31     }
32 }
33 
34 int main()
35 {
36     while(scanf("%lld",&n))
37     {
38         ans = 0;
39         if(n == 0) break;
40         for(int i = 0; i < n; i ++)
41             scanf("%lld",&a[i]);
42         mergesort(0,n-1);
43         printf("%lld\n",ans);
44     }    
45     return 0;
46 }
posted on 2012-09-14 12:56 BFP 阅读(138) 评论(0) 编辑收藏举报