[USACO17JAN]Balanced Photo平衡的照片

Posted 2020-11-13 66dzb

【TimeGate】

https://www.luogu.org/problem/P3608

【解题思路】

单点修改+区间查询，用树状数组来维护f数组即可

【code】

 1 #include <cstdio>
 2 #include <algorithm>
 3 using namespace std;
 4 typedef long long LL;
 5 struct Node{
 6     LL h;
 7     int cnt;
 8 }a[100005];
 9 LL ans;
10 LL b[100005],bit[100005],Maxn,n,p;
11 inline bool cmp(const Node &a,const Node &b){
12     return a.h>b.h;
13 }
14 int Sum(int x){
15     int sum=0;
16     for(int i=x;i>=1;i-=(i&(-i)))
17         sum+=bit[i];
18     return sum;
19 }
20 void Update(int x,int v){
21     for(int i=x;i<=n;i+=(i&(-i)))
22         bit[i]+=v;
23 }
24 int main(){
25     //freopen("3608.in","r",stdin);
26     //freopen("3608.out","w",stdout);
27     scanf("%lld",&n);
28     for(register int i=1;i<=n;i++){
29         scanf("%lld",&a[i].h);
30         a[i].cnt=i;
31     }
32     sort(a+1,a+n+1,cmp);
33     for(register int i=1;i<=n;i++)
34         b[a[i].cnt]=i;
35     for(register int i=1;i<=n;i++){
36         int l=Sum(b[i]);
37         int r=b[i]-l-1;
38         Update(b[i],1);
39         if(l>r*2||r>2*l)ans++;
40     }
41     printf("%d
",ans);
42     return 0;
43 }