ch_5501 环路运输

单调队列

zhk手写单调队列定义：

初始时  l=r=0

(l,r]  为有效元素

删除最左元素  ++l

删除最右元素  --r

队列有有效元素：l+1<=r ,即  l<r

取最左点  q[l+1]

取最右点  q[r]

#include<iostream> 
#include<cstdio>

#define ri register int
#define u int

namespace opt {
    
    inline u in() {
        u x(0),f(1);
        char s(getchar());
        while(s<'0'||s>'9') {
            if(s=='-') f=-1;
            s=getchar();
        }
        while(s>='0'&&s<='9') {
            x=(x<<1)+(x<<3)+s-'0';
            s=getchar();
        }
        return x*f;
    }
    
}

using opt::in;

#define NN 1000005

#include<algorithm>

namespace mainstay {
    
    u q[NN],a[NN],l,r,N,ans;
    
    inline void solve(){
        N=in();
        for(ri i(1);i<=N;++i) a[i]=a[i+N]=in();
        for(ri i(1);i<=(N<<1);++i){
            while(l+1<=r&&q[l+1]<i-(N>>1)) ++l;
            if(l+1<=r) ans=std::max(ans,a[q[l+1]]-q[l+1]+i+a[i]);
            while(l+1<=r&&a[q[r]]-q[r]<=a[i]-i) --r;
            q[++r]=i;
        } 
        std::cout<<ans;
    }
    
}

int main() {
    
    //freopen("x.txt","r",stdin);
    std::ios::sync_with_stdio(false);
    mainstay::solve();
    
}