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| #include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;
int n, ll, rr, a[500005], b[500005][19], mlg[500005], k;
long long ans=0, m;
struct Node{
int o, l, r, t, v;
}nd[2000005];
int query(int l, int r){
int t=mlg[r-l+1];
if(a[b[l][t]]>a[b[r-(1<<t)+1][t]]) return b[l][t];
else return b[r-(1<<t)+1][t];
}
bool cmp(Node a, Node b){
return a.v<b.v;
}
int main(){
cin>>n>>m;
ll = 1; rr = n;
for(int i=1; i<=n; i++){
scanf("%d", &a[i]);
a[i] += a[i-1];
b[i][0] = i;
}
for(int i=2; i<=n; i++) mlg[i] = mlg[i>>1] + 1;
for(int i=1; i<=18; i++)
for(int j=1; j+(1<<i)-1<=n; j++){
if(a[b[j][i-1]]>a[b[j+(1<<(i-1))][i-1]]) b[j][i] = b[j][i-1];
else b[j][i] = b[j+(1<<(i-1))][i-1];
}
for(int i=1; i+ll-1<=n; i++){
int l=i+ll-1, r=i+rr-1;
if(r>n) r = n;
int t=query(l, r);
nd[++k] = (Node){i, l, r, t, a[t]-a[i-1]};
push_heap(nd+1, nd+1+k, cmp);
}
while(m--){
Node x=nd[1];
pop_heap(nd+1, nd+1+k, cmp);
k--;
ans = x.v;
if(x.t!=x.l){
int t=query(x.l, x.t-1);
nd[++k] = (Node){x.o, x.l, x.t-1, t, a[t]-a[x.o-1]};
push_heap(nd+1, nd+1+k, cmp);
}
if(x.t!=x.r){
int t=query(x.t+1, x.r);
nd[++k] = (Node){x.o, x.t+1, x.r, t, a[t]-a[x.o-1]};
push_heap(nd+1, nd+1+k, cmp);
}
}
cout<<ans<<endl;
return 0;
}
|