能过样例 20pts

#include <bits/stdc++.h>

#define int long long

#define x first
#define y second

using namespace std;

const int N = 3e5 + 5;

typedef pair<int, int> PII;

int n, k;
int a[N], h[N];
struct node{
	int pre, nxt, val;
}l[N];
priority_queue<PII> Q;
int ans;

signed main(void) {
	cin >> n >> k;
	for (int i = 1; i <= n; i ++ ) cin >> a[i];
	for (int i = 1; i <= n; i ++ ) {
		l[i].val = a[i];
      		l[i].nxt = i + 1;
        	l[i].pre = i - 1;
		Q.push(make_pair(a[i], i));
	}
	
	while (k -- ) {
		auto t = Q.top(); Q.pop();
		if (h[t.y]) {
			k ++;
			continue;
		}
		if (t.x <= 0) break;
		ans += t.x;
		int left = l[t.y].pre, right = l[t.y].nxt;
		h[left] = 1, h[right] = 1;
		int u = l[left].val + l[right].val - l[t.y].val;
		l[t.y].pre = l[l[t.y].pre].pre, l[t.y].nxt = l[l[t.y].nxt].nxt;
		l[l[t.y].pre].nxt = t.y, l[l[t.y].nxt].pre = t.y;
		Q.push(make_pair(u, t.y));
	}
	
	cout << ans << '\n';
	
	return 0;
}