BZOJ1597 USACO2008土地购买

斜率优化DP。

 #include<bits/stdc++.h>
 using namespace std;
 const int N=5e5+;
 long long f[N],n,cnt,q[N];
 double eps=1e-;
 bool v[N];
 struct node{
     long long x,y;
     bool operator<(const node &b)const{
         if(x==b.x)return y<b.y;
         return x<b.x;
     }
 }a[N],b[N];
 double calc(int x,int y)
 {
     return (double)(f[x]-f[y])/(b[y+].y-b[x+].y);
 }
 void solve()
 {
     int l=,r=;q[]=;
     for(int i=;i<=cnt;++i)
     {
         while(l<r&&calc(q[l],q[l+])<=b[i].x)l++;
         f[i]=f[q[l]]+1ll*b[i].x*b[q[l]+].y;
         while(l<r&&calc(q[r-],q[r])>=calc(q[r],i))r--;
         q[++r]=i;
     }
     return;
 }
 int main()
 {
     scanf("%d",&n);
     for(int i=;i<=n;++i)
     {
         scanf("%lld%lld",&a[i].x,&a[i].y);
     }
     sort(a+,a++n);
     for(int i=;i<=n;++i)
     {
         while(cnt>&&a[i].y>=b[cnt].y)cnt--;
         b[++cnt]=a[i];
     }
     solve();
     printf("%lld\n",f[cnt]);
     return ;
 }