HDU 1394 Minimum Inversion Number

#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;
int n,c[5001],x,a[5001];
int add(int x){while(x<=n)c[x]++,x+=x&-x;}
int sum(int x){int s=0;while(x>0)s+=c[x],x-=x&-x;return s;}
int main(){
while(~scanf("%d",&n)){
int ans=0;
memset(c,0,sizeof(c));
for(int i=0;i<n;i++){
scanf("%d",&a[i]);
ans+=(i-sum(a[i]+1));
add(a[i]+1);
}int tmp=ans;
for(int i=0;i<n-1;i++){
tmp=tmp-a[i]+n-a[i]-1;
ans=min(ans,tmp);
}printf("%d\n",ans);
}
return 0;
}