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| #include <bits/stdc++.h>
#define pre(u) node[u].l
#define nxt(u) node[u].r
#define val(u) node[u].val
using namespace std;
const int maxn = 200005;
struct Node {
int l, r, val;
}node[maxn];
struct Heap {
priority_queue<pair<int, int> > a, b;
inline void push(pair<int, int> t) {a.push(t);}
inline void pop() {
while (b.size() && a.top() == b.top()) a.pop(), b.pop();
a.pop();
}
inline void erase(pair<int, int> t) {b.push(t);}
inline pair<int, int> top() {
while (b.size() && a.top() == b.top()) a.pop(), b.pop();
return a.top();
}
}q;
inline void del(int p) {
nxt(pre(p)) = nxt(p);
pre(nxt(p)) = pre(p);
}
int N, M;
int main() {
scanf("%d%d", &N, &M);
if (M * 2 > N) return puts("Error!"), 0;
for (register int i = 1; i <= N; ++i)
scanf("%d", &node[i].val),
node[i].l = i - 1, node[i].r = i + 1,
q.push(make_pair(node[i].val, i));
node[1].l = N, node[N].r = 1;
int ans = 0;
for (register int i = 1; i <= M; ++i) {
ans += q.top().first;
int p = q.top().second;
q.pop();
val(p) = val(pre(p)) + val(nxt(p)) - val(p);
q.erase(make_pair(val(pre(p)), pre(p))),
q.erase(make_pair(val(nxt(p)), nxt(p)));
q.push(make_pair(val(p), p));
del(pre(p)), del(nxt(p));
}
printf("%d", ans);
return 0;
}
|