bzoj1597 [Usaco2008 Mar]土地购买

题目链接

还是不太会斜率优化

果然我还是太弱了

 1 #include<algorithm>
 2 #include<iostream>
 3 #include<cstdlib>
 4 #include<cstring>
 5 #include<cstdio>
 6 #include<string>
 7 #include<cmath>
 8 #include<ctime>
 9 #include<queue>
10 #include<stack>
11 #include<map>
12 #include<set>
13 #define rre(i,r,l) for(int i=(r);i>=(l);i--)
14 #define re(i,l,r) for(int i=(l);i<=(r);i++)
15 #define Clear(a,b) memset(a,b,sizeof(a))
16 #define inout(x) printf("%d",(x))
17 #define douin(x) scanf("%lf",&x)
18 #define strin(x) scanf("%s",(x))
19 #define LLin(x) scanf("%lld",&x)
20 #define op operator
21 #define CSC main
22 typedef unsigned long long ULL;
23 typedef const int cint;
24 typedef long long LL;
25 using namespace std;
26 void inin(int &ret)
27 {
28     ret=0;int f=0;char ch=getchar();
29     while(ch<'0'||ch>'9'){if(ch=='-')f=1;ch=getchar();}
30     while(ch>='0'&&ch<='9')ret*=10,ret+=ch-'0',ch=getchar();
31     ret=f?-ret:ret;
32 }
33 struct xl
34 {
35     int x,y;
36     bool op < (const xl &a)const {return x==a.x?y<a.y:x<a.x;}
37 };
38 xl a[50050];
39 xl sta[50050];
40 int que[50050];
41 int top,n;
42 LL ans[50050];
43 double k(int a,int b)
44 {
45     return 1.*(ans[b]-ans[a])/(1.*(sta[a+1].y-sta[b+1].y));
46 }
47 int main()
48 {
49     inin(n);
50     re(i,1,n)inin(a[i].x),inin(a[i].y);
51     sort(a+1,a+n+1);
52     re(i,1,n)
53     {
54         while(top&&sta[top].y<=a[i].y)top--;
55         sta[++top]=a[i];
56     }
57     int l=0,r=0;
58     re(i,1,top)
59     {
60         while(l<r&&k(que[l],que[l+1])<sta[i].x)l++;
61         ans[i]=ans[que[l]]+(LL)sta[que[l]+1].y*sta[i].x;
62         while(l<r&&k(que[r],i)<k(que[r-1],que[r]))r--;
63         que[++r]=i;
64     }
65     printf("%lld",ans[top]);
66     return 0;
67 }

 

posted @ 2016-03-25 09:10  HugeGun  阅读(116)  评论(0编辑  收藏  举报