蓝题训练9.25P3195 [HNOI2008] 玩具装箱

P3195 [HNOI2008] 玩具装箱
https://www.luogu.com.cn/problem/P7323
Tag： 略
题意：略

题解：依旧斜率优化

参考代码

#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const ll maxn=50010;
ll f[maxn];
ll head,tail,n,L,a[maxn];
struct vec{
	ll id,x,y;
	ll operator()(ll v,ll u){
		return x*v+y*u;
	}
}q[maxn];
ll cross(vec a,vec b,vec c){
	c.x-=b.x;c.y-=b.y;
	b.x-=a.x;b.y-=a.y;
	return b.x*c.y-b.y*c.x;
}
void solve(){
	cin>>n>>L;
	for(int i=1;i<=n;i++) {
		cin>>a[i];
		a[i]+=a[i-1]+1;
	}
	L++;

		head=tail=0;
		q[0]={0,0,0};
		for(int i=1;i<=n;i++){
			while(head<tail&&q[head](2*(L-a[i]),1)>=q[head+1](2*(L-a[i]),1)){
				++head;
			}
			f[i]=q[head](2*(L-a[i]),1)+(a[i]-L)*(a[i]-L);
			vec x={i,a[i],f[i]+a[i]*a[i]};
			while(head<tail&&cross(q[tail-1],q[tail],x)<=0){
				--tail;
			}
			q[++tail]=x;
		}
	
	cout<<f[n]<<"\n";
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	ll T=1;
	while(T--) solve();
}

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