题解：
斜率优化dp
代码：
#include<bits/stdc++.h>
typedef long long ll;
const int N=;
using namespace std;
int n,l,r,q[N];
ll p[N],x[N],c[N],f[N],b[N],sum[N];
double slop(int k,int j)
{
return double(f[j]-f[k]+b[j]-b[k])/double(sum[j]-sum[k]);
}
int main()
{
scanf("%d",&n);
for (int i=;i<=n;i++)scanf("%d%d%d",&x[i],&p[i],&c[i]);
for (int i=;i<=n;i++)
{
sum[i]=sum[i-]+p[i];
b[i]=b[i-]+p[i]*x[i];
}
for (int i=;i<=n;i++)
{
while (l<r&&slop(q[l],q[l+])<x[i])l++;
int t=q[l];
f[i]=f[t]-b[i]+b[t]+(sum[i]-sum[t])*x[i]+c[i];
while (l<r&&slop(q[r-],q[r])>slop(q[r],i))r--;
q[++r]=i;
}
printf("%lld",f[n]);
return ;
}