HDU 1394 Minimum Inversion Number（逆序数）

 1 /*
 2 ** HDU 1394 Minimum Inversion Number
 3 ** Created by Rayn @@ 2014/04/14
 4 */
 5 #include <cstdio>
 6 #include <cstring>
 7 #include <algorithm>
 8 using namespace std;
 9 
10 const int MAX = 5010;
11 int arr[MAX], ans;
12 
13 int main()
14 {
15 #ifdef _Rayn
16     //freopen("in.txt", "r", stdin);
17 #endif
18 
19     int N;
20     while(scanf("%d", &N) != EOF && N)
21     {
22         for(int i=0; i<N; ++i)
23         {
24             scanf("%d", &arr[i]);
25         }
26         int sum = 0;
27         for(int i=0; i<N; ++i)
28         {
29             for(int j=i+1; j<N; ++j)
30             {
31                 if(arr[i] > arr[j])
32                         sum++;
33             }
34         }
35         ans = sum;
36         for(int i=0; i<N-1; ++i)
37         {
38             sum = (sum - arr[i]) + (N - arr[i] - 1);
39             ans = min(ans, sum);
40         }
41         printf("%d\n", ans);
42     }
43     return 0;
44 }