bzoj 1597: [Usaco2008 Mar]土地购买

 1 #include <bits/stdc++.h>
 2 #define LL long long
 3 #define lowbit(x) x&(-x)
 4 #define inf 0x3f3f3f3f
 5 #define eps 1e-5
 6 #define N 100005
 7 using namespace std;
 8 inline int ra()
 9 {
10     int x=0,f=1; char ch=getchar();
11     while (ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) f=-1; ch=getchar();}
12     while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘; ch=getchar();}
13     return x*f;
14 }
15 int n,tot;
16 LL x[N],y[N],f[N];
17 int q[N];
18 struct node{int x,y;}a[N];
19 bool cmp(node a, node b){return a.x==b.x?a.y<b.y:a.x<b.x;}
20 double slope(int a, int b){return (f[b]-f[a])/(y[a+1]-y[b+1]);}
21 int main(int argc, char const *argv[])
22 {
23     n=ra();
24     for (int i=1; i<=n; i++) a[i].x=ra(),a[i].y=ra();
25     sort(a+1,a+n+1,cmp);
26     for (int i=1; i<=n; i++)
27     {
28         while (tot && a[i].y>=y[tot]) tot--;
29         x[++tot]=a[i].x; y[tot]=a[i].y;
30     }
31     int l=0,r=0;
32     for (int i=1; i<=tot; i++)
33     {
34         while (l<r && slope(q[l],q[l+1])<x[i]) l++;
35         int t=q[l];
36         f[i]=f[t]+y[t+1]*x[i];
37         while (l<r && slope(q[r],i)<slope(q[r-1],q[r])) r--;
38         q[++r]=i;
39     }
40     printf("%lld\n",f[tot]);
41     return 0;
42 }