Bzoj 2058: [Usaco2010 Nov]Cow Photographs 题解

 1 #include <iostream>
 2 #include <cstdlib>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <queue>
 6 #include <algorithm>
 7 #include <cmath>
 8 #include <map>
 9 #include <set>
10 #define N 100005
11 using namespace std;
12 int n,a[N],b[N],dl[2*N];
13 int lowbit(int x)
14 {
15     return x&(-x);
16 }
17 void add(int x)
18 {
19     for(int i=x;i<=n;i+=lowbit(i))
20         b[i]++;
21 }
22 int get(int x)
23 {
24     int ans=0;
25     for(int i=x;i>0;i-=lowbit(i))
26         ans+=b[i];
27     return ans;
28 }
29 long long ans[N];
30 int main()
31 {
32     scanf("%d",&n);
33     for(int i=1;i<=n;i++) scanf("%d",&a[i]),dl[a[i]]=i;
34     for(int i=n;i>=1;i--)
35     {
36         ans[0]+=get(a[i]);
37         add(a[i]);
38     }
39     long long mn=ans[0];
40     for(int i=1;i<n;i++)
41     {
42         a[dl[i]]=n+i-1;
43         ans[i]=ans[i-1]-(dl[i]-1)+n-dl[i];
44         mn=min(mn,ans[i]);
45         dl[n+i-1]=i;
46     }
47     printf("%lld\n",mn);
48     return 0;
49 }