hdu1394 Minimum Inversion Number

#include<stdio.h>
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define maxn 5555
int n,x[maxn],sum[maxn],add=0;
int Pushup(int rt)
{
sum[rt]=sum[rt<<1]+sum[rt<<1|1];
}
int build(int l,int r,int rt)
{
int m=0;
if(l==r) {sum[rt]=0;return 0;}
m=(l+r)>>1;
build(lson);
build(rson);
Pushup(rt);
}
int query(int L,int R,int l,int r,int rt)
{
int m,temp=0;
if(L<=l&&r<=R) return sum[rt];
m=(l+r)>>1;
if(L<=m) temp+=query(L,R,lson);
if(m<R)  temp+=query(L,R,rson);
return temp;
}
int updata(int q,int l,int r,int rt)
{
int m;
if(l==r) {sum[rt]++;return 0;}
m=(l+r)>>1;
if(q<=m) updata(q,lson);
else updata(q,rson);
Pushup(rt);
}
int main()
{
freopen("hdu1394.in","r",stdin);
freopen("hdu1394.out","w",stdout);
int i,ans;
while(scanf("%d",&n)==1)
{
build(0,n-1,1);add=0;
for(i=1;i<=n;i++)
{
scanf("%d",&x[i]);
add=add+query(x[i]+1,n-1,0,n-1,1);
updata(x[i],0,n-1,1);
}
ans=add;
for(i=1;i<=n;i++)
{
add+=-x[i]+n-1-x[i];
ans=ans<add?ans:add;
}
printf("%d\n",ans);
}
return 0;
}