BZOJ3156: 防御准备

 1 #include<cstdio>
 2 
 3 #include<cstdlib>
 4 
 5 #include<cmath>
 6 
 7 #include<cstring>
 8 
 9 #include<algorithm>
10 
11 #include<iostream>
12 
13 #include<vector>
14 
15 #include<map>
16 
17 #include<set>
18 
19 #include<queue>
20 
21 #include<string>
22 
23 #define inf 1000000000
24 
25 #define maxn 1000000+5
26 
27 #define maxm 500+100
28 
29 #define eps 1e-10
30 
31 #define ll long long
32 
33 #define pa pair<int,int>
34 
35 #define for0(i,n) for(int i=0;i<=(n);i++)
36 
37 #define for1(i,n) for(int i=1;i<=(n);i++)
38 
39 #define for2(i,x,y) for(int i=(x);i<=(y);i++)
40 
41 #define for3(i,x,y) for(int i=(x);i>=(y);i--)
42 
43 #define mod 1000000007
44 
45 using namespace std;
46 
47 inline int read()
48 
49 {
50 
51     int x=0,f=1;char ch=getchar();
52 
53     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
54 
55     while(ch>=‘0‘&&ch<=‘9‘){x=10*x+ch-‘0‘;ch=getchar();}
56 
57     return x*f;
58 
59 }
60 int n,q[maxn];
61 ll a[maxn],f[maxn];
62 inline double k(ll i,ll j)
63 {
64     
65     return ((double)(f[i]+(i*i+i)/2-f[j]-(j*j+j)/2))/(double)(i-j);
66 }
67 
68 int main()
69 
70 {
71 
72     freopen("input.txt","r",stdin);
73 
74     freopen("output.txt","w",stdout);
75 
76     n=read();
77     for1(i,n)a[i]=read();
78     int l=1,r=1;
79     for1(i,n)
80     {
81         while(l<r&&k(q[l+1],q[l])<i)l++;
82         f[i]=f[q[l]]+(ll)(i-q[l])*(ll)(i-q[l]-1)/2+a[i];
83         while(l<r&&k(i,q[r])<k(q[r],q[r-1]))r--;
84         q[++r]=i;
85     }
86     cout<<f[n]<<endl;
87 
88     return 0;
89 
90 }