【HDU】1394 Minimum Inversion Number 
 1 #include<cstdio>
 2 #include<cstring>
 3 #define MIN(a,b) ((a)>(b)?(b):(a))
 4 #define MAXN 5010
 5 int tree[MAXN<<2],a[MAXN];
 6 inline void PushUp(int rt)
 7 {
 8     tree[rt]=tree[rt<<1]+tree[rt<<1|1];
 9 }
10 void Update(int x,int L,int R,int rt)
11 {
12     if(L==R)
13         tree[rt]=1;
14     else
15     {
16         int mid=(L+R)>>1;
17         if(mid>=x)
18             Update(x,L,mid,rt<<1);
19         else
20             Update(x,mid+1,R,rt<<1|1);
21         PushUp(rt);
22     }
23 }
24 int Query(int x,int y,int L,int R,int rt)
25 {
26     if(x<=L&&R<=y)
27         return tree[rt];
28     else
29     {
30         int mid,ans;
31         ans=0;
32         mid=(L+R)>>1;
33         if(x<=mid)
34             ans+=Query(x,y,L,mid,rt<<1);
35         if(y>mid)
36             ans+=Query(x,y,mid+1,R,rt<<1|1);
37         return ans;
38     }
39 }
40 int main()
41 {
42     int n,i,ans,temp;
43     while(~scanf("%d",&n))
44     {
45         memset(tree,0,sizeof(tree));
46         for(ans=i=0;i<n;i++)
47         {
48             scanf("%d",&a[i]);
49             a[i]++;
50             ans+=Query(a[i],n,1,n,1);
51             Update(a[i],1,n,1);
52         }
53         temp=ans;
54         for(i=0;i<n;i++)
55         {
56             temp+=n+1-(a[i]<<1);
57             ans=MIN(ans,temp);
58         }
59         printf("%d\n",ans);
60     }
61     return 0;
62 }
posted on 2012-05-21 11:16  DrunBee  阅读(346)  评论(0)  编辑  收藏  举报