洛谷1484 种树

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<queue>
 4 #define LL long long
 5 using namespace std;
 6 const int maxn=1000010;
 7 LL pre[maxn],nxt[maxn],a[maxn],n,m,x,ans=0;
 8 bool mark[maxn];
 9 priority_queue<pair<LL,LL>,vector<pair<LL,LL> > >q;
10 inline int read(){
11     int k=0,f=1; char c=getchar();
12     while(c<‘0‘||c>‘9‘)c==‘-‘&&(f=-1),c=getchar();
13     while(‘0‘<=c&&c<=‘9‘)k=k*10+c-‘0‘,c=getchar();
14     return k*f;
15 }
16 void del(int x){
17     mark[x]=1;
18     pre[nxt[x]]=pre[x]; nxt[pre[x]]=nxt[x];
19     pre[x]=nxt[x]=0;
20 }
21 int main(){
22     n=read(); m=read();
23     for(int i=1;i<=n;i++) a[i]=read(),q.push(make_pair(a[i],i));
24     if(m>n/2){puts("ERROR"); return 0;}
25     for(int i=1;i<=n;i++) pre[i]=i-1,nxt[i]=i+1; //pre[1]=n; nxt[n]=1;
26     for(int i=1;i<=m;i++){
27         while(mark[q.top().second]) q.pop();
28         int tmp=q.top().second; q.pop();
29         if(a[tmp]<0) break;
30         ans+=a[tmp]; 
31         a[tmp]=a[pre[tmp]]+a[nxt[tmp]]-a[tmp]; q.push(make_pair(a[tmp],tmp));
32         del(pre[tmp]); del(nxt[tmp]);
33     }
34     return printf("%lld\n",ans),0;
35 }