题目：
http://www.lydsy.com/JudgeOnline/problem.php?id=1096
题解：
#include<cstdio> #include<algorithm> #include<cstring> using namespace std; const int N=1e6+5; typedef long long ll; int n,q[N]; ll dp[N],c[N],x[N],p[N],sump[N],sumpx[N]; double calc(int k,int j) { return 1.0*(dp[j]-dp[k]+sumpx[j]-sumpx[k])/(sump[j]-sump[k]); } int main() { scanf("%d",&n); for(int i=1;i<=n;i++) scanf("%lld%lld%lld",&x[i],&p[i],&c[i]),sump[i]=sump[i-1]+p[i],sumpx[i]=sumpx[i-1]+p[i]*x[i]; int ql=0,qr=0; for(int i=1;i<=n;i++) { while(ql<qr &&calc(q[ql],q[ql+1])<(double)x[i]) ql++; int j=q[ql]; dp[i]=dp[j]+(sump[i]-sump[j])*x[i]-(sumpx[i]-sumpx[j])+c[i]; while(ql<qr &&calc(q[qr-1],q[qr])>calc(q[qr],i))qr--; q[++qr]=i; } printf("%lld ",dp[n]); return 0; }