*HDU 1394 经典逆序数的四种解法

 1 /*HDU1394暴力写法*/
 2 #include <iostream>
 3 #include <string.h>
 4 #include <stdio.h>
 5 
 6 using namespace std;
 7 
 8 int A[50005];
 9 int Low[50005],Up[50005];
10 int main(){
11     int n;
12     while(~scanf("%d",&n)){
13         int ans,sum=0;
14         for(int i=1;i<=n;i++){
15             scanf("%d",&A[i]);
16             for(int j=1;j<i;j++){
17                 if (A[j]>A[i]) sum++;
18             }
19         }
20         ans=sum;
21         for(int i=0;i<n;i++){
22             Low[i]=i;
23             Up[i]=n-i-1;
24         }
25         for(int i=1;i<=n-1;i++){
26             sum=sum+(Up[A[i]]-Low[A[i]]);
27             ans=min(sum,ans);
28         }
29         printf("%d\n",ans);
30     }
31     return 0;
32 }