[BZOJ1010]HNOI2008玩具装箱|斜率优化DP

第一次做这题的时候看的别人的博客，迷迷糊糊就过去了。。回来看发现不太懂，自己再学了学，理解得深了一点。。

我的笔记

别人的博客

#include<iostream>#include<cstdio>#include<memory.h>#include<cstdlib>#define ll long long#define q1 que[head]#define q2 que[head+1]#define t1 que[tail]#define t2 que[tail-1]using namespace std;int i,j,n,head,tail,c[50005],que[50005];ll dp[50005],f[50005],l,C;ll H(int i) {return (ll)f[i]*f[i]+2*f[i]*C+C*C;}ll G(int i) {return (ll)f[i]*f[i]-2*f[i]*C+dp[i];}ll get(int i){while (2*f[i]*(f[q2]-f[q1])>G(q2)-G(q1)&&tail-head>0) head++;return -2*f[q1]*f[i]+G(q1)+H(i);}void ins(int i){while (tail-head>0&&(G(i)-G(t1))*(f[t1]-f[t2])<(G(t1)-G(t2))*(f[i]-f[t1])) tail--;que[++tail]=i;}int main(){freopen("1010.in","r",stdin);scanf("%d%I64d",&n,&l);f[0]=dp[0]=0ll;C=-l-1;for (i=1;i<=n;i++){scanf("%d",&c[i]);f[i]=f[i-1]+(ll)c[i]+1;}head=tail=1;que[1]=0;que[++tail]=1;dp[1]=-2*f[0]*f[1]+G(0)+H(1);for (i=2;i<=n;i++){dp[i]=get(i);ins(i);}cout<<dp[n];}