BZOJ 1597: [Usaco2008 Mar]土地购买 动态规划 + 斜率优化

Code:

#include<bits/stdc++.h>
#define maxn 1000000
#define ll long long
#define x(i) (b[i+1])
#define y(i) (f[i])
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int A[maxn],arr[maxn],q[maxn],tot,head,tail;
ll a[maxn], b[maxn], f[maxn], u[maxn], v[maxn];
bool cmp(int i,int j)
{
    return u[i]==u[j]?v[i]<v[j]:u[i]<u[j];
}
double slope(int i,int j)
{
    return (double)(1.00*y(i)-y(j))/(double)(1.00*x(j)-x(i));
}
int main()
{
    // setIO("input");
    int n,i,j;
    scanf("%d",&n);
    for(i=1;i<=n;++i) scanf("%lld%lld",&u[i],&v[i]),A[i]=i;
    sort(A+1,A+1+n,cmp);
    for(i=1;i<=n;++i)
    {
        while(v[A[i]]>=b[tot]&&tot) --tot;
        ++tot, a[tot]=u[A[i]], b[tot]=v[A[i]];
    }
    n=tot,head=tail=0;
    for(i=1;i<=n;++i)
    {
        while(head<tail&&slope(q[head],q[head+1])<a[i]) ++head;
        f[i]=f[q[head]]+a[i]*b[q[head]+1];
        while(head<tail&&slope(q[tail], i)<slope(q[tail-1],i)) --tail;
        q[++tail]=i;
    }
    printf("%lld\n",f[n]);
    return 0;
}