BZOJ 2153 设计铁路

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 1000050
using namespace std;
long long n,m,t,r,sum1[maxn],sum2[maxn],f[maxn],mx=0,q[maxn],l=1;
long long get_x(long long x) {return x;}
long long get_y(long long x)
{
    if (!x) return 0;
    return f[x-1]-sum1[x-1]+sum2[x-1]*x+m;
}
int main()
{
    scanf("%lld%lld",&n,&m);
    for (long long i=1;i<=n;i++)
    {
        scanf("%lld%lld",&t,&r);
        mx=max(mx,t);sum1[t]+=r*t;sum2[t]+=r;
    }
    for (long long i=1;i<=mx;i++) sum1[i]+=sum1[i-1],sum2[i]+=sum2[i-1];
    q[l=r=1]=0;
    for (long long i=1;i<=mx;i++)
    {
        while (l<r && (get_x(q[r-1])-get_x(q[r]))*(get_y(q[r])-get_y(i))<(get_x(q[r])-get_x(i))*(get_y(q[r-1])-get_y(q[r]))) r--;
        q[++r]=i;
        while (l<r && sum2[i]*(get_x(q[l])-get_x(q[l+1]))<(get_y(q[l])-get_y(q[l+1]))) l++;
        f[i]=get_y(q[l])-q[l]*sum2[i]+sum1[i];f[i]=min(f[i],sum1[i]);
    }
    printf("%lld\n",f[mx]);
    return 0;
}