[日常训练]最大M子段和

#include<cmath>
#include<ctime>
#include<stack>
#include<queue>
#include<cstdio>
#include<vector>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#define N 100005
#define M -100000000000001LL
using namespace std;
typedef long long ll;
struct heap{
    ll k;int n;
}h[N],tmp;
ll a[N],num[N],sum,ans;
int lst[N],nxt[N],n,m,cnt;
inline bool cmp(ll x,ll y){
    return x>y;
}
inline bool chk(heap x,heap y){
    if(x.k!=y.k) return x.k<y.k;
    return x.n<y.n;
}
inline void swim(int i){
    heap a=h[i];int j=i>>1;
    while(j&&chk(a,h[j])){
        h[i]=h[j];num[h[i].n]=i;i=j;j>>=1;
    }
    h[i]=a;num[h[i].n]=i;
}
inline void sink(int i){
    heap a=h[i];int j=i<<1;
    while(j<=cnt){
        if(j<cnt&&chk(h[j+1],h[j])) ++j;
        if(chk(a,h[j])) break;
        h[i]=h[j];num[h[i].n]=i;i=j;j<<=1;
    }
    h[i]=a;num[h[i].n]=i;
}
inline void del(int u){
    if(!u||u>n) return;
    if(num[u]){
        if(num[u]==cnt) --cnt;
        else{
            h[num[u]]=h[cnt--];sink(num[u]);swim(num[u]);
        }
    }
    lst[nxt[u]]=lst[u];nxt[lst[u]]=nxt[u];
}
inline void init(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;++i){
        scanf("%lld",&a[i]);
        if(a[i]>=0LL){
            ++cnt;ans+=a[i];
        }
    }
    /*正数个数<=m*/
    if(cnt<=m){
        sort(a+1,a+1+n,cmp);
        for(int i=1;i<=m;++i)
            sum+=a[i];
        printf("%lld\n",sum);
        return;
    }
    cnt=0;
    for(int i=1;i<=n;++i){
        if(sum*a[i]<0LL){
            a[++cnt]=sum;sum=a[i];
        }
        else sum+=a[i];
    }
    a[++cnt]=sum;
    n=cnt;cnt=0;
    for(int i=1;i<=n;++i)
        if(a[i]>0) ++cnt;
    /*正数区间数<=m*/
    if(cnt<=m){
        printf("%lld\n",ans);return;
    }
    for(int i=1;i<=n;++i){
        lst[i]=i-1;nxt[i]=i+1;
    }
    lst[n+1]=n;nxt[0]=1;
    m=cnt-m;cnt=0;
    for(int i=1;i<=n;++i){
        h[++cnt].k=abs(a[i]);h[cnt].n=i;num[i]=cnt;swim(cnt);
    }
    while(m){
        tmp=h[1];h[1]=h[cnt--];sink(1);
        if(((!lst[tmp.n]||nxt[tmp.n]>n)&&a[tmp.n]<0)||!a[tmp.n]) continue;
        ans-=tmp.k;a[tmp.n]+=a[lst[tmp.n]]+a[nxt[tmp.n]];
        del(lst[tmp.n]);del(nxt[tmp.n]);
        h[++cnt].k=abs(a[tmp.n]);h[cnt].n=tmp.n;swim(cnt);
        --m;
    }
    printf("%lld\n",ans);
}
int main(){
    freopen("sequence.in","r",stdin);
    freopen("sequence.out","w",stdout);
    init();
    fclose(stdin);
    fclose(stdout);
    return 0;
}